The lifeforms known as Gadoll unexpectedly appeared as a danger to humanity in the far future. The last people on Earth are confined to the Tank, a lower area of the massive mobile fortress Deca-Dence. While the Gears who live on the upper floors are warriors who go out to fight as part of the Power, most Tankers are content to provide backline support, butchering Gadoll meat and reinforcing defenses. Natsume is one of those who would rather fight on the front lines; unafraid of her prosthetic right arm, she seeks to join the small number of Tanker soldiers who fight alongside the Gears. Despite her orphanage companions obtaining their employment assignments, Natsume's enlistment in the Power continues.