A nine-year-old boy Ren was an orphan, ran away from his foster parents, and wandered the streets of Tokyo. There, Tamon meets a great warrior, a bear-like monster from a parallel world, who has appeared to find a pupil. The pupil becomes Ren. In the world of monsters, the boy receives the name Devyata, and under the guidance of Medvezhuta begins training to become a master of martial arts.