Employees
| Concept | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2022-03-31 | As at 2022-03-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Employees | ||||||||||||
| Information about reporting company | ||||||||||||
| Information about employees of reporting company | ||||||||||||
| Number of employees | 
                                                101
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                407
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,374
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,374
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                175
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,866
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                164
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,451
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,532
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                144
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                142
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,705
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                24
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                37
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                565
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                565
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                504
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                7
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                614
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                677
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                734
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | — | — | 
                                                45.0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | — | — | 
                                                22.0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
| Average annual salary | — | — | — | — | 
                                                9,311,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — |