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 | ||||||||||
| Ordinary profit (loss) | — | 
                                                -1,426,891,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -1,325,760,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -964,064,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -859,372,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -1,552,230,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net assets | 
                                                1,232,656,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                791,198,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,233,161,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,078,727,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,056,188,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total assets | 
                                                1,474,155,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                906,817,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,324,352,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,161,192,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,162,132,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Net assets per share | 
                                                149.69
                                                
                                             | — | 
                                                123.91
                                                
                                             | — | 
                                                227.41
                                                
                                             | — | — | 
                                                390.87
                                                
                                             | 
                                                456.47
                                                
                                             | — | 
| Basic earnings (loss) per share | — | 
                                                -198.78
                                                
                                             | — | 
                                                -234.51
                                                
                                             | — | 
                                                -178.58
                                                
                                             | 
                                                -187.34
                                                
                                             | — | — | 
                                                -348.32
                                                
                                             | 
| Diluted earnings per share | — |  | — |  | — |  |  | — | — |  | 
| Equity-to-asset ratio | 
                                                0.836
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.870
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.931
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.961
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.951
                                                
                                                    
                                                        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 | — | 
                                                -1,279,615,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -1,303,049,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -940,399,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -726,649,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -1,649,277,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net cash provided by (used in) investing activities | — | 
                                                207,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -326,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -505,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -13,265,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net cash provided by (used in) financing activities | — | 
                                                1,853,195,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                882,617,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                119,857,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                875,313,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                99,920,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Cash and cash equivalents | 
                                                1,417,062,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                844,341,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,268,492,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,088,612,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,943,908,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Number of employees | 
                                                13
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                11
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                12
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                11
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                13
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Average number of temporary employees | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — |