Key Financial Data Of Reporting Company
| Concept | 2020-10-01 to 2020-12-31 | As at 2020-12-31 | 2019-10-01 to 2020-09-30 | As at 2020-09-30 | As at 2019-12-31 | 2019-10-01 to 2019-12-31 | 
|---|---|---|---|---|---|---|
| Key financial data of reporting company | ||||||
| Business results of reporting company | ||||||
| Net sales | 
                                                168,360,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,979,825,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                144,405,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Ordinary profit (loss) | 
                                                -161,616,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -583,378,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -178,762,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Profit (loss) | 
                                                -171,483,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -777,021,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -192,542,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Equity in earnings (losses) of affiliates if equity method is applied | 
                                                -9,127,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -19,069,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -13,627,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Share capital | — | 
                                                1,992,531,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,992,531,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,700,536,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total number of issued shares | — | 
                                                8,303,600
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
                                                8,303,600
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                6,681,100
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
| Net assets | — | 
                                                1,537,274,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,709,388,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,709,875,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total assets | — | 
                                                1,795,977,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,073,338,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,571,584,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Dividend paid per share |  | — |  | — | — |  | 
| Basic earnings (loss) per share | 
                                                -20.84
                                                
                                             | — | 
                                                -105.42
                                                
                                             | — | — | 
                                                -29.14
                                                
                                             | 
| Diluted earnings per share |  | — |  | — | — |  | 
| Equity-to-asset ratio | — | 
                                                0.856
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.824
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.665
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — |