In the face of the menacing Abyssal Fleet threatening humanity, the Kanmusu—girls embodying the spirits of Japanese warships—stand as humanity's final defense. Amidst their relentless battles, the Kanmusu teeter on the brink of destruction, particularly the ill-fated Mutsuki-class destroyer Kisaragi. After a daring night mission, Kanmusu from the Eighth Fleet chance upon Kisaragi, miraculously alive yet enigmatic, adrift at sea. Suspicious of her peculiar state and actions, the Kanmusu tread carefully. Soon, eerie voices and crimson waters plague the fleet, causing equipment malfunctions, with only Fubuki, the lead Fubuki-class destroyer, seemingly immune. As Fubuki and her comrades grapple with these inexplicable events, the unsettling truths about their world and the Abyssal Fleet gradually unfold. Despite the grim revelations, these valiant girls must forge ahead, determined to reclaim the ocean and safeguard their loved ones.