An alien invasion has ravaged Earth, culling humanity's numbers and leaving the world desperate for salvation. The first war against the Worms ended only after continents were shattered and most of the fighting men were lost. Three years later, the supposedly destroyed enemy shows signs of life again near Midway. Humanity's answer is the Sonic Divers, experimental flying exoskeletons built to meet the returning threat. Three young test pilots, Otoha Sakurano, Eika Ichijou and Karen Sonomiya, form this elite unit aboard the special vessel Koryu. When their carrier comes under attack, the girls must suit up and prove their unit can protect what remains of humanity. The result is a mecha sci-fi OVA about young pilots thrown into a war for survival.