Masayoshi tried to establish the foundation of his power by making relationships with influential people in the neighboring province through marriages, for example, a marriage to a daughter of FUJIWARA no Kiyohira of Oshu Fujiwara clan as his lawful wife.
また、正室には奥州藤原氏の藤原清衡の女を娶るなど、隣国の有力者との婚姻も結びその勢力基盤の確立に努めている。