With the seas under constant threat from the hostile "Abyssal Fleet," a specialized naval base is established to counter them. Rather than standard naval weaponry, however, the base is armed with "Kanmusu"—girls who harbor the spirits of Japanese warships—possessing the ability to don weaponized gear that allows them to harness the powerful souls within themselves. Fubuki, a young Destroyer-type Kanmusu, joins the ba...