He was born as a child of Shotokui KOSE no Oama, a member of the powerful KOSE clan, whose brother was Daishii (Fifth Rank) Sadaijin (Minister of the Left) KOSE no Tokuta in the Asuka Period.
飛鳥時代の有力氏族巨勢氏の一族小徳位巨勢大海（大紫位左大臣巨勢徳多の兄弟）の子として生まれる。