In a near-future world ravaged by rising sea levels due to global warming, a formidable armada called the Fleet of Fog emerges with advanced warships, each housing a unique 'Mental Model' representing the ship's core. These models, bound by the Admiralty Code, enforce a strict blockade to restrict human sea travel. Enter Gunzou Chihaya, a former marine academy student, who chances upon I-401 and its enigmatic Mental Model, Iona, breaking ranks to aid humanity. With this unexpected allegiance, Gunzou and his comrades establish the daring privateer group, Blue Steel, determined to defy the Fleet of Fog and pave a path towards peace amidst perilous waters.