His father Imperial Prince Otomo (who would later become Emperor Junna) was the son of Emperor Kanmu and his wife FUJIWARA no Tabiko, meaning that he was not a son by an empress like Emperor Heizei and Emperor Saga, who were the sons of the Empress (FUJIWARA no Otomuro), and thus strayed from the heir to the imperial throne according to Emperor Kanmu's policy.
父親の大伴親王（当時、後の淳和天皇）は、桓武天皇の子であると言っても夫人藤原旅子の子であり、皇后（藤原乙牟漏）所生の平城天皇・嵯峨天皇両天皇、いわゆる「后腹」の親王による皇位継承を目指した桓武天皇の方針からすれば皇位継承から外れる存在であった。