Key Financial Data Of Group
| Concept | As at 2024-03-31 | 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 | As at 2020-03-31 | 2019-04-01 to 2020-03-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|
| Key financial data of group | |||||||||||
| Business results of group | |||||||||||
| Net sales | — | — | 
                                                72,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                5,280,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                15,408,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,504,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                11,300,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Ordinary profit (loss) | — | — | 
                                                -1,158,929,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -1,473,774,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -1,481,945,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -1,738,636,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -1,823,996,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net assets | 
                                                978,987,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,567,541,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,531,475,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,537,642,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,235,237,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total assets | 
                                                1,230,257,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,701,444,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,771,202,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,749,428,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,474,639,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Net assets per share | 
                                                13.52
                                                
                                             | — | — | 
                                                24.60
                                                
                                             | — | — | 
                                                45.40
                                                
                                             | — | 
                                                69.10
                                                
                                             | 
                                                75.49
                                                
                                             | — | 
| Basic earnings (loss) per share | — | — | 
                                                -18.21
                                                
                                             | — | 
                                                -24.90
                                                
                                             | 
                                                -28.55
                                                
                                             | — | 
                                                -36.14
                                                
                                             | — | — | 
                                                -44.20
                                                
                                             | 
| Diluted earnings per share | — | — |  | — |  |  | — |  | — | — |  | 
| Equity-to-asset ratio | 
                                                0.777
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.909
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.905
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.937
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.915
                                                
                                                    
                                                        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 | — | — | 
                                                -1,156,920,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -1,204,401,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -1,512,022,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -1,769,848,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -1,784,461,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net cash provided by (used in) investing activities | — | — | 
                                                -7,648,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -1,760,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -17,566,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -36,211,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -106,879,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net cash provided by (used in) financing activities | — | — | 
                                                690,959,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                432,104,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                569,226,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,053,090,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                8,521,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Cash and cash equivalents | 
                                                1,057,360,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,530,969,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,305,026,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,265,388,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,018,356,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Number of employees | 
                                                24
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                32
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                38
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                44
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                44
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Average number of temporary employees | 
                                                4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — |