Under the influence of the Chinese books like "History of the Later han Dynasty" and "Bai-Shi Wen Ji," the original tale, which had been passed on by word of mouth, was once written down in Chinese, and then it seems to have been rewritten in kana later.
元々、口承説話として伝えられたものが『後漢書』や『白氏文集』など漢籍の影響を受けて一旦は漢文の形で完成されたが、後に平仮名で書き改められたと考えられている。