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 2024-03-31 | As at 2023-03-31 | As at 2022-03-31 | As at 2021-03-31 | 
|---|---|---|---|---|---|---|---|---|---|
| Employees | |||||||||
| Information about reporting company | |||||||||
| Information about employees of reporting company | |||||||||
| Number of employees | 
                                                170
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                51
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                93
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                106
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                420
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                394
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                387
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                381
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                377
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | — | — | 
                                                44.3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
| Average length of service (Years) | — | — | — | — | 
                                                15.9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
| Average annual salary | — | — | — | — | 
                                                7,604,695
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — |