The world is falling apart and Casshern is to blame. He is said to have killed a robot named "Luna" and by doing so unleashed a plague referred to as "ruin". But Casshern has no recollection of committing such an act, none the less both the humans and sentient robots hold him accountable. Now he must struggle to unravel what has truly happened to the world to be able to make a mends for his sins.