The Imperial seal supposedly found by Sonken, Hakufu's father, it is a large jade seal that serves a role similar to a Royal Crown. Whoever carries it is granted authority over all the other nations but it expectedly becomes a big target for everyone. Seito Academy originally held it before Toutaku stole it, but it eventually went to Ryomou from Ryofu who passed to Saji then finally back to Seito.
It is still in the hands of Seito, protected by Kan'u and Chou'un.