In the 91st century, mankind built space colonies and moved its residence to space. However, the environmental control system of the colony group "Little Japan" located on the other side of the moon LaGrange 2 suddenly shut down, and its core "Dire 51" started attacking humanity. Dire 51 attacked other colony groups violently, collecting materials and debris and strengthening and expanding its own colonies. The huge and strange appearance of the enemies eyes became a sign of hatred and fear among people. Though the cause of Dire 51's malfunction was hurriedly investigated by many research teams, no conclusion could be found about the cause. Meanwhile, Dire 51 develops a powerful armor and begins its attack against Earth. The battle on Earth intensifies, and the situation gets into a staggering state. In order to defeat the attacking forces, Earth finally places its last bet on the MUSHA unit.