When Masakado took the name of the 'New Emperor' himself, Masayori was appointed as governor of Shimotsuke Province, but in February, 940, when Masakado was defeated and killed in the war against TAIRA no Sadamori and FUJIWARA no Hidesato, his power also instantly collapsed, and Masayori himself later was defeated in Sagami Province.
将門が「新皇」を僭称すると下野国守に任ぜられるが、天慶3年（940年）2月、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、後日将頼も相模国にて討たれた。