Arturia Pendragon finds herself in an unexpected situation. Summoned not as a Servant, but as the ship spirit of HMS King Arthur, she navigates a realm where magic and naval warfare collide. Caught between her identity as the Once and Future King and her new existence as a ship spirit, Arturia must unravel the mystery of her summoning.

In the darkness of the sea, the abyss slumbers, biding its time until the proper hour. Its enemies defeated, its existence forgotten, humanity would be unprepared for the coming storm. Yet in the fires of the Fourth Holy Grail War hope awakens, and stumbling onto a young Shirou Emiya, she makes her choice. And everything changes. "Admiral, aircraft carrier Kaga, awaiting orders."

A young girl who wishes for the most powerful Servant to serve by her side gets what she asked for... though who said only humans can become legends?