When Masakado started to call himself 'the new emperor,' Masatame was appointed to Shimousa no kami; however, his power declined at a stretch after Masakado died in the battle with TAIRA no Sadamori and FUJIWARA no Hidesato on March 30, 940, and eventually Masatame, his families and retainers were killed one after another.
将門が「新皇」を僭称すると下総守に任ぜられるが、天慶3年（940年）2月14日、将門が平貞盛・藤原秀郷らとの戦いによって敗死すると勢力は一気に瓦解し、次々と一族郎党は討たれた。