Nearly 200 years after the destruction of humanity in World War III, Roue lives a happy life exploring the ruins of civilization with her "uncle," a robot named Zett. But when their peaceful life is threatened, Roue must trust the mysterious robot Chrome to bring her family together again.

Hildr, a command-class military gear, has just won 50 back-to-back fights inside the warrior coliseum of Valhalla and now faces her 51st opponent--Chrome. As the two face off, Roue is forced to watch helplessly from the confines of a storage room on the lower levels. But while both Chrome's and Roue's attention is focused on the battle at hand, Valhalla's ruler begins to hatch his own sinister scheme. Unbeknownst to her, Roue holds the fate of Valhalla in her hands, and danger is creeping ever closer!