Exploring space in 1967, humanity meets and battles the hostile alien race Beta, who defeat all human defenses and land on Earth in 1973. By 1998, the Beta have overcome fierce resistance to conquer half of Eurasia. Japan trains high school students such as Yui Takamura as potential battle mech pilots. When the Beta attack despite Japan's strong combat forces and U.S. military help, the situation is so desperate that reservist trainees Yui and her female friends must go into battle.
