In the distant future, Earth has devolved into a wasteland, and humanity as we know it has perished. All that's left are sentient robots. They were supposed to be immortal—until the one named Luna died and the Ruin began. Their bodies will rust, and there will be no way to repair them. The robots are now left to contemplate their deaths, only kept alive by the rumor that if they eat the one known as Casshern, they will gain immortality. Casshern has no idea about his past, why he exists, or what he is, but he must find out or face the constant agony of being pursued by robots who don't want to die. Casshern follows death wherever he goes.