According to "Nihonshoki," during the war against the Yamato regime's army Tsukushinokimiiwai said to the shogun, Omi no Kenu, "you and I once lived under the same roof," and it is considered that Iwai moved from Kyushu region to the Yamato Province when he was young and served Yamoto Okimi with Kenu and others.
『日本書紀』には、ヤマト政権軍と交戦した際、将軍の近江毛野に対して磐井が「かつては同じ釜の飯を食べた仲ではないか」と呼びかけたとする記述があり、磐井は若い頃、九州からヤマトへのぼり、ヤマト大王の元で毛野らとともに仕えた経験があると考えられている。