Therefore, when the Hatakeyama clan had an internal fight over the leadership of the family, Katsumoto and Mochitoyo YAMANA, who had become his father-in-law, supported Yasaburo HATAKEYAMA (Mochikuni’s adopted son) in driving out Yoshinari HATAKEYAMA (Mochikuni’s real son, who had been recommended by Mochikuni) in order to bring Mochikuni down, since he was Katsumoto’s political enemy.
そのため、畠山氏で家督をめぐる内紛が起こったときには、政敵である持国を失脚させるため、舅にあたる山名持豊ともに畠山弥三郎（持国養子）を支援して持国の推す畠山義就（持国実子）を追放に追い込んだ。