Seventeen-year-old Jirou Azuma lives a quiet life with his grandfather, utilizing his supernatural ability to speak with animals to befriend and protect them. Both Jirou and his grandfather are descendants of a long-standing shinobi clan, training in combat to keep the art of battle alive within their family. Jirou's life is thrown into upheaval after rescuing a seemingly normal black cat, Ragou, only to discover that the cat is actually a mononoke—a demonic spirit that has long been at war with mankind. When a hostile mononoke comes looking for Ragou, Jirou uses his shinobi training to jump to the cat's defense, but immediately suffers a mortal wound. Faced with the decision of whether or not to devour Jirou's fading energy and restore himself to full power, Ragou instead chooses to give