In the distant future, humanity is faced with a sudden threat from Gadoll lifeforms. The remaining humans reside in the Tank, a lower level within the colossal mobile fortress named Deca-Dence. While those on the upper floors, known as Gears, are the warriors fighting against Gadolls as part of the Power, most Tankers prefer to stay behind and offer support from within. Natsume, however, has an unwavering determination to join the few Tanker soldiers on the front lines, despite her prosthetic right arm. Though her peers have been assigned roles in the orphanage, Natsume is still waiting for approval to join the Power. Awaiting her big break, Natsume starts working in Kaburagi's armor repair team. Kaburagi, a tough and indifferent leader, recognizes Natsume's potential to disrupt the current world's order, and takes her under his wing to prepare her for the role of the game-changer.