Key Financial Data Of Group
| Concept | As at 2024-03-31 | 2023-04-01 to 2024-03-31 | As at 2023-03-31 | 2022-04-01 to 2023-03-31 | As at 2022-03-31 | 2021-04-01 to 2022-03-31 | 2020-04-01 to 2021-03-31 | As at 2021-03-31 | As at 2020-03-31 | 2019-04-01 to 2020-03-31 | 
|---|---|---|---|---|---|---|---|---|---|---|
| Key financial data of group | ||||||||||
| Business results of group | ||||||||||
| Net sales | — | 
                                                100,402,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                94,201,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                71,932,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                67,947,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                85,759,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Ordinary profit (loss) | — | 
                                                -879,380,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -689,604,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -481,681,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -410,107,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -834,362,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net assets | 
                                                1,398,344,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,396,545,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,152,154,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,083,713,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                485,889,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total assets | 
                                                1,693,810,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,566,650,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,300,530,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,118,626,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                547,889,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Net assets per share | 
                                                110.94
                                                
                                             | — | 
                                                201.13
                                                
                                             | — | 
                                                268.05
                                                
                                             | — | — | 
                                                128.86
                                                
                                             | 
                                                79.05
                                                
                                             | — | 
| Basic earnings (loss) per share | — | 
                                                -93.69
                                                
                                             | — | 
                                                -66.93
                                                
                                             | — | 
                                                -54.47
                                                
                                             | 
                                                -59.03
                                                
                                             | — | — | 
                                                -136.95
                                                
                                             | 
| Diluted earnings per share | — |  | — |  | — |  |  | — | — |  | 
| Equity-to-asset ratio | 
                                                0.7818
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.9215
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.9550
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.9661
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.8868
                                                
                                                    
                                                        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
                                                    
                                                
                                             | 
| Net cash provided by (used in) operating activities | — | 
                                                -833,898,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -564,274,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -476,842,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -422,836,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -608,524,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net cash provided by (used in) investing activities | — | 
                                                -150,343,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -212,989,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -33,868,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -2,824,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -3,409,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net cash provided by (used in) financing activities | — | 
                                                63,943,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -20,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,647,548,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,011,040,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Cash and cash equivalents | 
                                                1,541,419,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,444,934,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,214,852,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,069,300,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                482,464,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Number of employees | 
                                                25
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                24
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                21
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                19
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                21
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Average number of temporary employees | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — |