The Boy and the Beast Vol. 1 (manga)

Set in the human realm (Tokyo's Shibuya ward) and the bakemono realm ("Juutengai"). In these two worlds, which must not intersect, there lives a lonely boy and a lonely bakemono. One day, the boy gets lost in the bakemono world, becomes the disciple of the bakemono Kumatetsu, and is renamed Kyuuta. Fleeing tragedy and mistreatment, the young boy named Ren hides among the crowds in Tokyo's busy Shibuya ward. His efforts to run away are more successful than he realizes when he ends up in the world of the beasts! The rough-living bear named Kumatetsu gives Ren a new life and a new name, but is Kumatetsu really up to the job of being a mentor?