In the year 2040, global warming has caused the poles, glaciers and mountain ice caps to melt and submerge the entire world. The surviving 100,000 inhabitants now live aimlessly on the manmade Aquapolice City which floats on top of the ocean. Lately, they have come under attack from an unidentified robotic life-form called SPOOK. It is up to the Aquapolice air defense force to repel the invaders, but their overwhelming numbers are too much and gradually they are being pushed towards defeat and annihilation. That’s when a mysterious girl named Nagi appeared with the super-weapon robot called GrandBlue Aerials.