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 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 | As at 2021-03-31 | As at 2021-03-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Employees | ||||||||||||||||||
| Information about reporting company | ||||||||||||||||||
| Information about employees of reporting company | ||||||||||||||||||
| Number of employees | 
                                                89
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                659
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                131
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                125
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                439
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                89
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                400
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                614
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                591
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                632
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                661
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                583
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                608
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                697
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                752
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                671
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                207
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,584
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                32
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                32
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,345
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                207
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,279
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,518
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,478
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,538
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,240
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,162
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                632
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                672
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                804
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                743
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | — | — | — | — | — | — | — | 
                                                43.9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | — | — | — | — | — | — | — | 
                                                9.5
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | — | — | — | — | — | — | — | 
                                                4,989,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — |