The constant danger posed by the alien Abyssal Fleet puts humanity at risk, relying solely on the Kanmusu - young women embodying the spirits of Japanese warships - to defend them. These valiant heroines struggle against a seemingly inevitable fate, facing death at sea. One such ship, the Mutsuki-class destroyer Kisaragi, meets a tragic end. Yet, after a successful nocturnal operation, the Kanmusu of the Eighth Fleet spot Kisaragi still alive but unconscious, drifting on the ocean's surface. Despite Kisaragi's strange demeanor and the strange circumstances, the Kanmusu proceed with caution. Other ships in the fleet begin hearing unexplainable voices and encountering waters tinged with crimson that damages their equipment. Surprisingly, Fubuki, the lead ship of the Fubuki-class destroyers, remains unscathed. As the Kanmusu confront this mysterious situation, they uncover the harsh realities of their existence and the danger posed by the Abyssal Fleet. Nonetheless, these courageous girls push forward, determined to protect their loved ones and free the sea from the enemy's grasp.