In an unspecified future, the orbital space colony OCC launches a sudden invasion of Earth, catching the Earth Defense Allied Forces (EDAF) badly off-guard. With conventional forces shattered, EDAF starts pulling in anyone who can fly — including Delta Squadron, a notorious group of disgraced and misfit pilots that nobody else wanted. Despite their reputation, Delta Squadron's efforts begin turning the tide against OCC, earning them the particular hatred of the colony's elite experimental unit. As the EDAF pushes closer to victory, an even larger threat emerges: an organization based on Mars has been using OCC as a proxy and is now moving to destroy Earth itself through the orbital platform.