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.

Following the advice of new friends, Roue and Chrome set off to find Heaven Land, a gear utopia, in order to revive Uncle Zett. But when a threatening gear blocks their path, Chrome unknowingly takes on a vicious combat form that frightens Roue. What other secrets might Chrome have that he doesn't even know himself? And when their next lead on Heaven Land brings them to Valhalla, a coliseum of warriors, what horrors will Chrome unleash when he's forced to fight once more?