is a Japanese manga series produced by Ark Performance and serialized in Shōnen Gahosha's Young King Ours. 25 tankōbon volumes have been released and an anime series by Sanzigen aired from October to December 2013. The same studio also produced two films based on the series, released in January and October 2015.
Plot
Due to global warming and rising sea levels in the early 21st century, much of Earth's landmass has been lost. In 2039, fleets of powerful sentient warships, armed with advanced technology and possibly 'alien' weaponry, mysteriously appear and devastate the world's naval forces. These ships, collectively known as 'The Fleet of Fog', impose a worldwide naval and aerial blockade, preventing humanity from both traveling the oceans and to other nations. During the blockade, the Fleet of Fog created Mental Models, humanoid avatars containing a ship's Union core, as a means to develop self cultivation and to overcome their lack of creative thinking of tactics that humans possessed, which at the same time made the Mental Models develop their own unique personality.
In 2056, 17 years after the blockade began, Gunzō Chihaya, a former student of the Japanese National Marine Academy, is the captain of a small group of privateers called the 'Blue Steel'. The Blue Steel are infamous for possessing a Fog submarine, the I-401, along with its Mental Model Iona, who defected to the human side. Due to I-401's technology and Gunzō's tactical skills, the Blue Steel have not only survived several encounters with the Fleet of Fog but managed to sink one of their most powerful warships.
Gunzō and his crew are hired by a faction of the Japanese government to deliver the prototype of the vibration warhead, a powerful weapon that may finally allow mankind to fight back against the Fog, to the United States. The United States is the only country with the resources and capability to mass-produce the weapon system. However, the Blue Steel will face obstacles on their journey not only from the Fleet of Fog and their human allies, but from other governments and factions with their own agendas. Along the way they will also gain allies of their own from both sides, increasing their chances against seemingly overwhelming odds.
Characters
Blue Steel Fleet
The main protagonist, captain of the I-401 and leader of the Blue Steel Fleet. He is not interested in destroying the Fleet of Fog, but to be on equal footing with them so negotiations leading to peace can be realized. / I-401
The Mental Model (human avatar) of the submarine I-401 who left the Fog to become Gunzō's vessel of her own volition. In the Cadenza movie, it was revealed that the supreme flagship Yamato was defeated by her sister Musashi after she went on a rampage and had carried her last wish into Iona herself, therefore the reason for carrying dual cores inside her, which was to be Gunzō's vessel and negotiate with the Fleet of Fog to end the war, which was Gunzō's father's actions. After defeating Musashi by becoming one with Yamato, she disappears as she had served her purpose and bids Gunzō farewell. Over the course of the series, Iona has developed human emotions which led the other Fog vessels to classify her as a traitor, but those who came in contact with her have either defected to the Fog, joined the Blue Steel fleet, or had the ship's mental model experience errors. After defeating Hyuga, the crew of the I-401 salvaged and mounted the battleship's Super Gravitational Cannon onto the bow of the submarine. In the manga, she has been shown to use the M6A Seiran dive bombers that her real life counterpart was equipped with, making her the only Fog vessel ever seen to utilize aircraft.
First Mate of I-401 who always wears a helmet supposedly due to allergies. He is Gunzō's closest friend and always knows what the latter is thinking. He wields the position as helmsman and executive-officer.
Weapons officer of I-401. Unlike the rest of his friends in the Blue Steel who were the top ten during their Naval Academy days, Kyōhei was in the 200th place. He also owns a huge collection of gravure idols merchandise and usually is the first to panic when the crew finds themselves in a pinch.
Engineer of I-401 who operates the engines of the vessel.
Sonar operator of I-401, she is also a capable soldier able to take down several troops with skill and strategy only. Her past is a mystery but it is known she's been to Taiwan.