In this world, there is a world of humans and also another separate world. The world of Beasts.

Shibuya in the human world and Jutengai in the Beast world.

The story starts with a lonely boy and a loner Beast that live in these two unconnected worlds.

One day, a boy encounters a Beast, Kumatetsu, and decides to go live in the world of Beasts in order to get strong. He becomes Kumatetsu’s apprentice, who gives him a new name, Kyuta. At first, they clash about everything, but their extraordinary life and training together help both of them mature, and gradually a bond develops between them just like a real father and son.

One day, when Kyuta has grown up to be a robust young man, he accidentally wanders back to Shibuya from Jutengai and meets schoolgirl Kaede. His encounter with Kaede, who teaches him about a new world and its values, makes him start wondering in which world he really belongs.