In a busy Tokyo street, a boy called Ren stands alone. He looks at his surroundings with hate and fury. He steals some food and goes to an abandoned corner to eat it. Two hooded figures approach him. One of the figures lifts his head and Ren looks, in horror, that the figure is a beast. The beast, Kumatetsu, asks Ren if he wants to become his apprentice. Ren doesn't say anything and Kumatetsu leaves. After the shock wears off, Ren follows Kumatetsu and enters the Beast Kingdom where beasts live. After a while, Ren becomes Kumatetsu's apprentice and helps his master perfect his technique so he can become Grandmaster and in the process, learn to let go of his anger and discover the meaning of family.
