The world has been consumed by a desperate, thirty-year war against the BETA, an alien species that invaded Earth in 1973. Amidst this turmoil, high school student Takeru Shirogane abruptly wakes from a harrowing nightmare depicting humanity's total defeat. He soon realizes that the dream was actually a memory of his life in an alternate universe. In that timeline, the Alternative V project was enacted, launching hundreds of thousands of people into space as a final measure to save humanity, while the remaining billion on Earth faced a brutal fate. Determined to alter this bleak future, Takeru enlists at a military base located in Yokohama, which is his former high school. There, he succeeds in persuading Professor Yuuko Kouzuki, the base's vice-commander and head of the Alternative IV project, to prevent Alternative V from occurring. To guarantee the success of Alternative IV, Takeru must pilot massive humanoid machines known as Tactical Surface Fighters (TSF) alongside his fellow cadets. However, he has only two months to finish his training and leverage his partial knowledge of the future, or the impending tragedy will unfold.