Key Financial Data Of Reporting Company
| Concept | 2024-04-01 to 2025-03-31 | As at 2025-03-31 | As at 2024-03-31 | 2023-04-01 to 2024-03-31 | As at 2023-03-31 | 2022-04-01 to 2023-03-31 | 2021-04-01 to 2022-03-31 | As at 2022-03-31 | 2020-04-01 to 2021-03-31 | As at 2021-03-31 | 
|---|---|---|---|---|---|---|---|---|---|---|
| Key financial data of reporting company | ||||||||||
| Business results of reporting company | ||||||||||
| Net sales | 
                                                120,375,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                100,402,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                94,201,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                71,932,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                67,947,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Ordinary profit (loss) | 
                                                -829,829,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -879,380,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -689,604,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -481,681,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -410,107,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Profit (loss) | 
                                                -904,800,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -1,104,460,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -786,999,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -599,023,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -413,216,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Equity in earnings (losses) of affiliates if equity method is applied | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Share capital | — | 
                                                2,437,908,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,971,019,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,939,252,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,939,252,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                604,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Total number of issued shares | — | 
                                                14,749,500
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                11,936,400
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
                                                11,759,400
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                11,759,400
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
                                                8,386,400
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
| Net assets | — | 
                                                1,432,406,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,398,344,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,396,545,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,152,154,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,083,713,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Total assets | — | 
                                                1,818,837,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,693,810,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,566,650,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,300,530,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,118,626,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net assets per share | — | 
                                                91.74
                                                
                                             | 
                                                110.94
                                                
                                             | — | 
                                                201.13
                                                
                                             | — | — | 
                                                268.05
                                                
                                             | — | 
                                                128.86
                                                
                                             | 
| Dividend paid per share |  | — | — |  | — |  |  | — |  | — | 
| Interim dividend paid per share |  | — | — |  | — |  |  | — |  | — | 
| Basic earnings (loss) per share | 
                                                -63.41
                                                
                                             | — | — | 
                                                -93.69
                                                
                                             | — | 
                                                -66.93
                                                
                                             | 
                                                -54.47
                                                
                                             | — | 
                                                -59.03
                                                
                                             | — | 
| Diluted earnings per share |  | — | — |  | — |  |  | — |  | — | 
| Equity-to-asset ratio | — | 
                                                0.7440
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.7818
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.9215
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.9550
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.9661
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Rate of return on equity | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        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 | 
                                                -719,485,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -833,898,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -564,274,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -476,842,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -422,836,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Net cash provided by (used in) investing activities | 
                                                -75,157,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -150,343,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -212,989,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -33,868,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -2,824,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Net cash provided by (used in) financing activities | 
                                                923,381,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                63,943,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -20,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,647,548,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,011,040,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Cash and cash equivalents | — | 
                                                1,667,921,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,541,419,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,444,934,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,214,852,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,069,300,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Number of employees | — | 
                                                32
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                25
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                24
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                21
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                19
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | — | 
                                                2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Total shareholder return | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Total return on share price index | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             |