It is unknown exactly when he became a demon and joined the Twelve Demonic Moons, but the impetus for this decision was the realization that people with the mark do not live to be 25 years old. 60 years later, on the night of the blood moon, he met his brother Yoriichi Tsugikuni, who almost cut off his head, but died of old age at the last moment.

Three hundred years ago, Kokushibo met a demon hunter who ate demon flesh to increase his powers. Kokushibo defeated him by cutting him in two.