After the death of Takesada, he succeeded to the head of the Dewa Kiyohara clan and adopted KIYOHARA no Narihira, the alleged second son of TAIRA no Yasutada, a family of the Taira clan, who was the Kokushi (provincial governor) of Dewa Province.
武貞の死後出羽清原氏を嗣ぎ、出羽国の国司であった平氏の一門、平安忠の次男と言われる清原成衡を養子に迎えた。