This is a certain world. In this world, monsters of the seas called "Abyssal Ships" are menacing the globe.

And yet, because of these monsters, those who would protect Humanity, the young girls named "Shipgirls" exist. These girls' days are those of battling the Abyssal Ships - protecting the people.

However, on a certain day, the situation changed - the Abyssal Fleet suddenly became stronger.

The cause for the sudden change was that a great evil King from another dimension lent his power to the Enemy.

With the war situation worsening, a certain Naval Base knew of the existence of but a single person who could defeat this great King.

That person was the Hero who opposed the great evil King's many ambitions.

And so, those girls pleaded that Hero for help. And that Hero's name was...