Key Financial Data Of Reporting Company
| Concept | As at 2024-12-31 | As at 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | As at 2022-12-31 | 2022-01-01 to 2022-12-31 | As at 2022-12-31 | 2022-01-01 to 2022-12-31 | 2021-01-01 to 2021-12-31 | As at 2021-12-31 | As at 2021-12-31 | 2021-01-01 to 2021-12-31 | 2020-01-01 to 2020-12-31 | As at 2020-12-31 | 2020-01-01 to 2020-12-31 | As at 2020-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Key financial data of reporting company | ||||||||||||||||||||||||||
| Business results of reporting company | ||||||||||||||||||||||||||
| Net sales | — | — | 
                                                542,056,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                636,235,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                1,625,889,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,468,204,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,386,748,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,216,066,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,931,718,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,017,529,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,133,346,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,042,960,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Ordinary profit (loss) | — | — | 
                                                -2,072,150,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -2,080,739,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                -1,126,283,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -1,176,623,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -1,278,820,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -1,357,020,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -548,843,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -522,992,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -1,077,096,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -1,096,348,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Profit (loss) | — | — | 
                                                -2,168,495,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
                                                -1,184,953,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                -1,405,357,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -556,425,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                -1,129,612,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Share capital | — | 
                                                2,447,707,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,076,474,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,382,246,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,056,953,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                558,829,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Total number of issued shares | — | 
                                                19,107,500
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | 
                                                17,151,900
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                14,218,300
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                13,313,400
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | — | 
                                                12,407,100
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
| Net assets | — | 
                                                2,198,126,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                2,475,354,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,877,535,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,624,863,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,641,844,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,439,714,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                4,194,643,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                4,315,572,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,741,428,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,824,010,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Total assets | — | 
                                                2,491,642,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                2,772,115,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                4,349,891,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                4,086,919,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                4,266,453,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                4,046,289,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                5,305,486,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,432,560,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                4,748,867,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                4,835,356,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net assets per share | — | 
                                                115.11
                                                
                                             | — | — | — | — | — | — | — | 
                                                129.62
                                                
                                             | — | 
                                                226.16
                                                
                                             | — | 
                                                211.43
                                                
                                             | 
                                                255.04
                                                
                                             | — | 
                                                240.82
                                                
                                             | — | — | 
                                                314.45
                                                
                                             | 
                                                323.54
                                                
                                             | — | — | 
                                                301.39
                                                
                                             | — | 
                                                308.05
                                                
                                             | 
| Dividend paid per share | — | — |  | — | — | — | — | — | — | — | — | — |  | — | — | — | — |  |  | — | — | — | — | — |  | — | 
| Interim dividend paid per share | — | — |  | — | — | — | — | — | — | — | — | — |  | — | — | — | — |  |  | — | — | — | — | — |  | — | 
| Basic earnings (loss) per share | — | — | 
                                                -121.08
                                                
                                             | 
                                                -121.64
                                                
                                             | — | — | — | — | — | — | 
                                                -68.62
                                                
                                             | — | 
                                                -70.53
                                                
                                             | — | — | 
                                                -99.10
                                                
                                             | — | 
                                                -103.20
                                                
                                             | 
                                                -43.83
                                                
                                             | — | — | 
                                                -42.10
                                                
                                             | 
                                                -90.33
                                                
                                             | — | 
                                                -91.84
                                                
                                             | — | 
| Diluted earnings per share | — | — |  |  | — | — | — | — | — | — |  | — |  | — | — |  | — |  |  | — | — |  |  | — |  | — | 
| Equity-to-asset ratio | — | 
                                                0.882
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                0.893
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.891
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.887
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.850
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.846
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.789
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.793
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.787
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.790
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Rate of return on equity | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Price-earnings ratio | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Payout ratio | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Net cash provided by (used in) operating activities | — | — | — | 
                                                -1,374,806,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                -1,677,464,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                -708,390,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                -1,536,612,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -1,260,972,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
| Net cash provided by (used in) investing activities | — | — | — | 
                                                -13,060,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                -11,376,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                -125,696,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                -41,677,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -70,433,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
| Net cash provided by (used in) financing activities | — | — | — | 
                                                567,441,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                1,182,027,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                367,006,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                1,064,987,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                724,423,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
| Cash and cash equivalents | — | — | — | — | — | — | — | — | — | 
                                                2,108,484,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,889,101,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,379,048,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                3,817,834,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                4,299,142,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Number of employees | 
                                                7
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                60
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                33
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                34
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                20
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                22
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                7
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                63
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                67
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                64
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                65
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                62
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                61
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                64
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                61
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                64
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                10
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                10
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Total shareholder return | — | 
                                                0.1413
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | 
                                                0.2459
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.2449
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.5191
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | 
                                                0.5709
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
| Total return on share price index | — | 
                                                1.8246
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | 
                                                1.5148
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                1.1810
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                1.2107
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | 
                                                1.0739
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — |