known since childhood as a person of genius , imperial prince kazurawara , who was also a founder of the taira clan , celebrated his coming of age along with prince otomo (later emperor junna ), a half-brother by the same father , in 789 . 平氏の祖で、幼少から俊秀として知られており、798年(延暦17年)、異母兄弟の大伴皇子(後の淳和天皇)と共に元服。