Escaping tragedy and mistreatment, a young boy named Ren conceals himself within the crowds of Tokyo's bustling Shibuya ward. His attempt to flee proves more successful than he anticipates when he finds himself in the world of the beasts! A rough-living bear named Kumatetsu provides Ren with a new life and a new name—Kyuuta—but is Kumatetsu truly capable of serving as a mentor?