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 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 | 
                                                40
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                103
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                83
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                105
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                79
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                105
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                40
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                248
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                327
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                228
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                307
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                79
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                312
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                293
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                288
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                304
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                293
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                271
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                286
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                263
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | — | — | — | — | — | — | — | — | 
                                                41.6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | — | — | — | — | — | — | — | — | 
                                                14
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average length of service (Months) | — | — | — | — | — | — | — | — | — | — | 
                                                0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | — | — | — | — | — | — | — | — | 
                                                6,640,855
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — |