In the near future, mankind was driven away from the seas and landmasses were isolated from each other with the advent of the "Fleet of Fog", All controlled ships which destroyed all opposition turning the world into turmoil. Years later, the Japanese Government is about to launch an unmanned cargo shuttle into orbit when the Fleet of Fog ship Nagara appears to prevent it. The launch is a success when the human-crewed Fog submarine I-401 defeats the enemy by request of the government. After the battle, the I-401's captain Gunzō Chihaya reminisce with its mental model, a human-shaped avatar…