Employees
| Concept | 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 | 
                                                3,430
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,430
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,254
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,135
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,317
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,380
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,848
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,450
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,928
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,853
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,407
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                455
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                455
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                134
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                492
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                492
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                356
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                353
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                177
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | 
                                                30
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average age (Months) | — | — | 
                                                9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | 
                                                4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Months) | — | — | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | 
                                                5,331,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — |