For nine-year-old Ren, things could hardly be worse. His mother has passed away in a traffic accident, his father is nowhere to be found, and his extended family is cold and distant. In the beast realm of Shibuten, the fierce warrior Kumatetsu is certainly feared, but not especially liked or respected. When Ren gets lost in a maze of alleyways and finds himself in the strange land of Shibuten, fate brings these two stubborn and fierce-willed souls together.