大友氏
In 804, Kūkai took part in a government-sponsored expedition to China, led by Fujiwara no Kadanomaro, in order to learn more about the "Mahavairocana Tantra". Scholars are unsure why Kūkai was selected to take part in an official mission to China, given his background as a private monk who was not sponsored by the state. Theories include family connections within the Saeki-Ōtomo clan, or connections through fellow clergy or a member of the Fujiwara clan.