2040 A.D., the world condition continues to deteriorate. Fighting for very limited living resources, World War III had broken among the major forces. The great war exhausted almost all regular energy sources of the world, human civilization was mostly destroyed. People who survived the cataclysm reunited to find new energy sources. During which, they found the so-called Document of Code51, in which a mystery energy substance Code51 has been revealed. With its discovery, mechs were made with this new energy. Warlords rose, factions formed. The union is as fragile as post-apocalyptic humanity. With these giant war gears, factions conflicted for exploiting Code51, another great war is breeding on the bruised earth…