Takashi YOSHIDA states that the reason Daio and Tenno stood aloof from 'sei' (family name) system by not having it was because Wakoku (country of Wa) left the Chinese Sakuho system at the end of the 5th century, and was not taken into the system as Wakoku-o even during the Reign of Empress Suiko at the beginning of the 7th century.
吉田孝は、倭国が5世紀末に中国の冊封体制から離脱し、7世紀初頭の推古朝でも倭国王に冊封されなかったことが、大王天皇が姓を持たず「姓」制度を超越し続けたことにつながったとしている。