A shadowy organization called the D.A.S. triggered ecological collapse by activating magnetic weapons designed to melt the polar ice caps, submerging most of the world beneath water. Humanity's scattered survivors cluster atop the few remaining structures, but the D.A.S.—having anticipated the catastrophe—maintains brutal control through an iron military grip and devastating weaponry. When intelligence reveals the D.A.S. is constructing an even more lethal superweapon called Yugusukyuure, oppressed survivors band together to launch a covert resistance, commandeering an experimental submarine named the Granvia as their instrument of liberation. The Granvia must navigate treacherous enemy-controlled waters, penetrate D.A.S. strongholds, and assault the organization's headquarters itself, systematically dismantling every weapon in the arsenal to free what remains of civilization.