Key Financial Data Of Group
| Concept | 
                                    
                                        As at 2024-09-30  | 
                            
                                
                                    
                                        2024-04-01 to 2024-09-30  | 
                            
                                
                                    
                                        2023-04-01 to 2024-03-31  | 
                            
                                
                                    
                                        As at 2024-03-31  | 
                            
                                
                                    
                                        As at 2023-09-30  | 
                            
                                
                                    
                                        2023-04-01 to 2023-09-30  | 
                            
                        
|---|---|---|---|---|---|---|
| Key financial data of group | ||||||
| Business results of group | ||||||
| Net sales | — | 
                                        
                                             
                                                5,632,744,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                9,354,195,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
                                        
                                             
                                                4,326,222,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Ordinary profit (loss) | — | 
                                        
                                             
                                                443,637,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                -186,071,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
                                        
                                             
                                                -369,473,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Profit (loss) attributable to owners of parent | — | 
                                        
                                             
                                                458,304,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                -408,659,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
                                        
                                             
                                                -396,162,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Comprehensive income | — | 
                                        
                                             
                                                574,028,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                -371,057,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
                                        
                                             
                                                -369,430,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Net assets | 
                                        
                                             
                                                8,058,026,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
                                        
                                             
                                                7,484,017,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                7,485,670,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
| Total assets | 
                                        
                                             
                                                15,703,014,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
                                        
                                             
                                                15,977,394,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                15,693,008,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
| Basic earnings (loss) per share | — | 
                                        
                                             
                                                32.19
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                -28.70
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
                                        
                                             
                                                -27.82
                                                
                                             
                                        
                                     | 
                                
                            
| Equity-to-asset ratio | 
                                        
                                             
                                                0.513
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
                                        
                                             
                                                0.468
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                0.477
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
| Net cash provided by (used in) operating activities | — | 
                                        
                                             
                                                848,365,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                451,871,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
                                        
                                             
                                                221,881,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Net cash provided by (used in) investing activities | — | 
                                        
                                             
                                                -282,254,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                -633,760,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
                                        
                                             
                                                -335,821,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Net cash provided by (used in) financing activities | — | 
                                        
                                             
                                                -622,494,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                144,425,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
                                        
                                             
                                                -169,045,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Cash and cash equivalents | 
                                        
                                             
                                                2,383,569,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
                                        
                                             
                                                2,494,032,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                2,228,167,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — |