The world has been attacked by gigantic monsters, you as a part of the Earth's Defence Force, EDF, must protect civilians from these monsters. Pick your class, be a Wing Diver which is a squad that fully consists of girls who fly, their armor is light which allows them to fly around and move easily, be a air raider, fencer, or a pale wing, which is basically a Wing Diver but better I guess. (I haven't played much of the game) or you can be a ranger that is basically a normal soldier.