Key Financial Data Of Group
| Concept | 2023-04-01 to 2023-12-31 | As at 2023-12-31 | 2023-10-01 to 2023-12-31 | As at 2023-03-31 | 2022-04-01 to 2023-03-31 | As at 2022-12-31 | 2022-04-01 to 2022-12-31 | 2022-10-01 to 2022-12-31 | 
|---|---|---|---|---|---|---|---|---|
| Key financial data of group | ||||||||
| Business results of group | ||||||||
| Revenue | 
                                                5,886,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,050,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                7,937,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                5,504,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,798,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Profit (loss) before tax | 
                                                -82,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                156,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                12,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Profit (loss) | 
                                                -469,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                450,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                7,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Profit (loss), attributable to owners of parent | 
                                                -475,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -88,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                450,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                7,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                37,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Comprehensive income | 
                                                -112,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                1,124,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                7,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Comprehensive income, attributable to owners of parent | 
                                                -119,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                1,124,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                7,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Equity attributable to owners of parent | — | 
                                                5,862,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,579,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,457,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Total assets | — | 
                                                12,690,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                8,074,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                6,472,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Basic earnings (loss) per share | 
                                                -5.03
                                                
                                             | — | 
                                                -0.87
                                                
                                             | — | 
                                                39.36
                                                
                                             | — | 
                                                0.08
                                                
                                             | 
                                                0.41
                                                
                                             | 
| Diluted earnings (loss) per share | 
                                                -5.03
                                                
                                             | — | — | — | 
                                                4.95
                                                
                                             | — | 
                                                0.08
                                                
                                             | — | 
| Ratio of owners' equity to gross assets | — | 
                                                0.461
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.4433
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.380
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
| Cash flows from (used in) operating activities | 
                                                -75,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                231,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                188,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Cash flows from (used in) investing activities | 
                                                -2,373,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                -61,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -70,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Cash flows from (used in) financing activities | 
                                                3,562,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                85,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                9,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Cash and cash equivalents | — | 
                                                2,740,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,627,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,498,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — |