Key Financial Data Of Reporting Company
| Concept | As at 2024-12-31 | 2024-01-01 to 2024-12-31 | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | 2022-01-01 to 2022-12-31 | As at 2022-12-31 | As at 2021-12-31 | 2021-01-01 to 2021-12-31 | 2020-01-01 to 2020-12-31 | As at 2020-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|
| Key financial data of reporting company | ||||||||||
| Business results of reporting company | ||||||||||
| Net sales | — | 
                                                54,446,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                61,112,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                374,477,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                708,245,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                137,484,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Ordinary profit (loss) | — | 
                                                -869,747,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -586,187,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -433,165,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                144,914,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -327,492,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Profit (loss) | — | 
                                                -872,238,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -589,211,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -473,962,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                142,905,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -329,501,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Equity in earnings (losses) of affiliates if equity method is applied | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Share capital | 
                                                1,364,728,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,283,445,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,272,005,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                100,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                100,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Total number of issued shares | 
                                                8,184,800
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                7,894,300
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
                                                7,773,300
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                1,001
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                1,001
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
| Net assets | 
                                                2,542,406,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,203,469,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,769,801,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,900,114,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,549,458,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Total assets | 
                                                3,518,001,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                4,214,809,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                4,815,337,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,646,232,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,196,213,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net assets per share | 
                                                304.60
                                                
                                             | — | — | 
                                                405.71
                                                
                                             | — | 
                                                484.88
                                                
                                             | 
                                                -5,183.91
                                                
                                             | — | — | 
                                                -5,469.44
                                                
                                             | 
| Dividend paid per share | — |  |  | — |  | — | — |  |  | — | 
| Interim dividend paid per share | — |  |  | — |  | — | — |  |  | — | 
| Basic earnings (loss) per share | — | 
                                                -108.34
                                                
                                             | 
                                                -75.42
                                                
                                             | — | 
                                                -177.67
                                                
                                             | — | — | 
                                                285.53
                                                
                                             | 
                                                -658.34
                                                
                                             | — | 
| Diluted earnings per share | — |  |  | — |  | — | — |  |  | — | 
| Equity-to-asset ratio | 
                                                0.709
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.760
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.783
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.718
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.705
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Rate of return on equity | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.083
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Price-earnings ratio | — | 
                                                
                                                
                                                    
                                                        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 | — | 
                                                -760,553,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -562,296,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -403,596,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                161,537,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -294,001,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Net cash provided by (used in) investing activities | — | 
                                                -8,637,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -19,474,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -430,674,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -50,583,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -264,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Net cash provided by (used in) financing activities | — | 
                                                -52,012,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                18,236,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,658,538,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                229,206,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                488,905,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Cash and cash equivalents | 
                                                2,052,570,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,873,773,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,437,307,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,613,040,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,272,879,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Number of employees | 
                                                21
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                21
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                21
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                22
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                19
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Total shareholder return | 
                                                0.347
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.586
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Total return on share price index | 
                                                0.882
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.967
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             |