When Kyuta, a young orphan living on the streets of Shibuya, stumbles into a fantastic world of beasts, he's taken in by Kumatetsu, a gruff, rough-around-the-edges warrior beast who's been searching for the perfect apprentice. Despite their constant bickering, Kyuta and Kumatetsu begin training together and slowly form a bond as surrogate father and son. But when a deep darkness threatens to throw the human and beast worlds into chaos, the strong bond between this unlikely pair will be put to the ultimate test-a final showdown that will only be won if the two can finally work together using all of their combined strength and courage.