Since 1973, an invasion of aliens upon Earth known as BETA has driven human civilization to destruction. In order to defend themselves from this enormous mass of enemy force, mankind has developed large humanoid arms called Tactical Surface Fighters and deployed them to its defense lines through out the world. However, its efforts could only slow down the impending defeat, and mankind has been forced to abandon the major areas of the Eurasian Continent. For 30 years, they have been caught in an endless war against BETA without any hopes of victory.