In February 941, the senior commander of Sumitomo's army, FUJIWARA no Tsunetoshi, defected and joined the Imperial army, which then attacked Sumitomo's base on Hiburi Island.
天慶4年（941年）2月、純友軍の幹部藤原恒利が朝廷軍に降り、朝廷軍は純友の本拠日振島を攻め、これを破った。