When human beings were ruled by robots originally made by human beings, a girl, Luna, appeared. People asked her for help, calling her a sun named moon. The ruler, Braking Boss, was afraid of her. He ordered three robots, Casshern, Dio, and Leda, to kill her. Eventually, she was killed by Casshern, and the world headed for ruination due to the secret of Luna. Several hundreds years later, the world is now in a state of ruin where nothing can reproduce. Although robots were thought to exist forever, death comes to them because they cannot replace their parts, and gradually their bodies are eroded by rust or some other cause. Buildings cannot keep their shapes, some of them collapse, some of them are deformed, and most of the earth has turned into wasteland. Meanwhile, Casshern, who had been lost since he killed Luna, appears. He has lost his memory and doesn’t even know who he is. However, there are people who attack him calling his name.