Arpeggio of Blue Steel: Ars Nova

In 2039, rising sea levels caused by severe global warming have swallowed much of the world’s land. A mysterious fleet of heavily armed warships appears, crushing naval forces worldwide. Calling themselves the Fleet of Fog, these ships possess "Mental Models"-humanoid avatars that embody their core consciousness, each with distinct personalities but all obeying a shadowy directive known as the Admiralty Code. The fleet enforces a strict blockade, cutting off humanity’s access to the oceans. Seventeen years later, Gunzou Chihaya, a former National Marine Academy student, discovers the submarine I-401 and its Mental Model, Iona, who for unknown reasons aligns with humans. Seeing a chance to break the blockade, Gunzou and his friends form a rogue crew called the Blue Steel, embarking on a perilous mission to challenge the Fleet of Fog and reclaim the seas.