According to the "Mutsuwaki" (Tales of Mutsu), in the opening skirmish of the Former Nine Years' War, Mutsu FUJIWARA no Narito attacked the Akita Jonosuke TAIRA no Shigenari as well as Yoriyoshi ABE, and in December 1051 was defeated in 'the Battle of Onikiribe'; this particular Akita Jonosuke, TAIRA no Shigenari, was the same TAIRA no Shigenari (though the "Shige" in his name was written differently) who was the son of the Yogo Shogun TAIRA no Koreshige, and Shigenari's descendants began calling themselves the Jo (castle) clan.
『陸奥話記』には、前九年の役の前哨戦として陸奥藤原登任は秋田城介平重成と安倍頼良を攻め、1051年（永承6年）11月の「鬼切部の戦」で敗北したとあるが、この秋田城介平重成は余五将軍平維茂の子の平繁成でありその子孫は城氏を名乗る。