Key Financial Data Of Reporting Company
| Concept | As at 2023-12-31 | 2023-10-01 to 2023-12-31 | 2023-04-01 to 2023-12-31 | As at 2023-03-31 | 2022-04-01 to 2023-03-31 | 2022-04-01 to 2022-12-31 | As at 2022-12-31 | 2022-10-01 to 2022-12-31 | 
|---|---|---|---|---|---|---|---|---|
| Key financial data of reporting company | ||||||||
| Business results of reporting company | ||||||||
| Net sales | — | — | 
                                                4,279,043,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                5,475,278,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                4,108,591,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Ordinary profit (loss) | — | — | 
                                                454,244,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                592,281,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                438,420,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Profit (loss) | — | — | 
                                                335,845,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                401,538,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                299,131,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Equity in earnings (losses) of affiliates if equity method is applied | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Share capital | 
                                                377,525,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                377,525,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                377,525,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total number of issued shares | 
                                                3,975,300
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                3,975,300
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                3,975,300
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
| Net assets | 
                                                3,811,828,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,634,991,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,532,584,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total assets | 
                                                5,938,420,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                5,768,040,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                5,631,108,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Dividend paid per share | — | — |  | — | 
                                                40.00
                                                
                                             |  | — | — | 
| Basic earnings (loss) per share | — | 
                                                28.08
                                                
                                             | 
                                                84.49
                                                
                                             | — | 
                                                101.01
                                                
                                             | 
                                                75.25
                                                
                                             | — | 
                                                26.39
                                                
                                             | 
| Diluted earnings per share | — | — |  | — |  |  | — | — | 
| Equity-to-asset ratio | 
                                                0.642
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.630
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.627
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — |