Heart Gear, Volume 4 (Heart Gear #22-29)

In a postapocalyptic future, a human girl and an android travel the world in search of a mythical utopia to protect those they love.

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.

General Wodan has been waiting centuries for the one thing he needs to make his dreams of the ultimate command a reality - a human biosignature. And now that Roue has fallen into his lap, he's able to rewrite the base program of every gear in Valhalla and force them to fight according to his will. The general has declared war, and Chrome must emerge victorious to have any hope of saving Roue before it's too late!