Employees
| Concept | 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 | 
                                                141
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                114
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                940
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                810
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                776
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                899
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                901
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                775
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                744
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                870
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                848
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                725
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | — | 
                                                44
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average age (Months) | — | — | — | 
                                                9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | — | 
                                                15
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Months) | — | — | — | 
                                                6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | — | 
                                                9,803,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — |