Since 1973, an invasion of aliens known as BETA upon Earth is driving human civilization into nearly collapse. Facing an enormous mass of enemy force, mankind has developed large humanoid arms called as Tactical Surface Fighters and deployed them to its defense lines through out the world. In 2001, the Imperial Japan faces difficulties in the development of a next-generation main Tactical Surface Fighters (TSF) as it defends the front lines of the Far East. Yui Takamura, a surface pilot of the Imperial Royal Guards of Japan, and her group of recruits, becomes the last line of defense.