Following a prolonged battle and sustaining a fatal injury, Aoi and his devoted retainer Kazuha sealed the chaos king, a demonic entity that dwells within human hearts... yet in their final moments, another of Aoi's retainers betrays them, binding Aoi and Kazuha's souls to reincarnate together so they may continue fighting the chaos king across all their lives. Centuries later, what unfolds now that both have been reborn as boys and the chaos king is on the verge of awakening?