In 1467, when the Onin no Ran (Rebellion of Onin) broke out, Mochikiyo joined the East forces led by Katsumoto HOSOKAWA along with Takatada TAGA to lead some 10,000 soldiers in battle against the West forces at Shioya, Keikain, in the capital city, and at Ichijo-omiya.
1467年（応仁元年）に応仁の乱が起こると、細川勝元の率いる東軍に家臣で従弟の多賀高忠と共に一万余騎を率いて属し、洛中の花開院塩屋、一条大宮などで西軍と戦う。