Heart Gear, Vol. 6 (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 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.

Roue, Chrome, and Rock have been taken in by Heaven Land’s retrieval team, the Donkeys. They seem friendly enough, but Chrome isn’t quite ready to let his guard down yet. The group decides to take the shortest route to Heaven Land, only to be attacked by a massive underwater creature! The Donkeys entrust Chrome with a weapon of massive firepower, but will it be enough to take down the creature and save them all?