When his father, TAIRA no Shigemori, who had been supposed to succeed Taira no Kiyomori, died of disease in July 1179 and TAIRA no Munemori took over as the head of the clan, Koremori and the other sons of Shigemori were put in a delicate position in the clan.
治承3年（1179年）7月、平清盛の後継者と目されていた父・平重盛が病死し、叔父の平宗盛が平氏の棟梁となると、維盛ら重盛の息子達は平氏一門で微妙な立場となる。