When Shirou Emiya died, he became a Heroic Spirit and joined the Throne of Heroes. Summoned as a Servant by the Counter Force, he now finds himself in a world of Shipgirls and Abyssals during the early Abyssal War. The Abyssals won't know what hit 'em when faced with Servants, and possibly Ship-Servant hybrids.

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?