According to "Nihonshoki," Iwai had been plotting a rebellion for a long time but he could not actually do it; however, Shiragi heard of the plot and then they bribed Iwai and suggested to raise a rebellion against the Yamato regime.
『日本書紀』は、磐井はかねてより反逆の企てを抱いていたものの実行に移せないでいたが、それを知った新羅は磐井へ賄賂を送り、ヤマト政権への反逆を勧めたとしている。