Heart Gear, Vol. 1 (manga)

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 civilisation 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.

After Roue accidentally activates Chrome without a base program, what's essentially his soul, she and Uncle Zett invite him into their makeshift family and encourage him to choose his own purpose. But when an insane machine attacks their home, will Chrome survive, much less find his purpose?