This is a story about a Royal Navy submarine named HMS Seal that got capture by the Germans during World War 2 during the Northern Europe Invasion. After failure attempt to bring him back to service; they decide to abandon him at the edge of the dockyard in Kiel. He thought that he would be trap alone until he meet with a German Heavy Cruiser named Admiral Hipper for decommission; she was the only friend during the times of war for him until Allied bombing destroyed both him and her. This is the story when HMS Seal will reunite with his friend Admiral Hipper in the world of Azur Lane.