Human survivors live inside Deca-Dence, a moving fortress that protects them from creatures called Gadoll. Its warriors, the Gears, fight outside while the Tankers keep life running within it. Natsume is a Tanker who wants to join the fighting, but her first job places her under the unsentimental armour repairman Kaburagi.
Work on the fortress’s outer shell makes the division between support labour and combat difficult to keep at a safe distance. When a Gadoll battle reaches their job, Natsume sees that the apparently unmotivated repairman can fight. Her wish to learn and his habit of refusing larger hopes bring two different responses to the same dangerous world into contact.
Natsume’s tool and work clothes belong to the role she has actually been assigned, even while she looks beyond it. Repairing armour helps the fortress survive, yet it does not satisfy her wish to take part in its defence as a warrior. Her early encounter with Kaburagi places that ambition inside a working relationship, where learning what another person can do may change what she thinks is possible for herself.