Rainbow Island, one of the several islands in this world governed by martial artists, is the stage of an incredible event. A newborn infant, Hei, is saved from a tragic ending and raised by a spirit beast spider. Under these unusual circumstances, Hei ends growing up with the body of a human but the mind of a spirit beast. However, this world is filled with conflicts, and his vision about spirit beast differs by the rest of the world. So, in order to protect his family, he decides to become a martial artist, beginning a journey that would bring him toward the peak of martial artist society while discovering the concealed story of the world.