According to "Nihonshoki" (Chronicles of Japan), Emperor Tenchi nominated his own younger brother, Prince Oama, to Togu (the Crown Prince); however, having doted so much on his own son, Emperor Tenchi broke the promise with his brother and appointed his son, Prince Otomo, to the Crown Prince.
『日本書紀』には、天智天皇は実弟・大海人皇子を東宮（皇太子）に任じていたが、天智天皇は我が子可愛さの余り、弟との約束を破って大友皇子を皇太子と定めたと記されている。