In the Onin War, Kuninobu like his older brother Nobukata, joined the East squad led by Katsumoto HOSOKAWA and fought bravely with the West squad including Shigeyori TOKI.
応仁の乱では兄の信賢同様に細川勝元の東軍に属して、土岐成頼らの西軍と戦うなど奮戦している。