Takes place at the end of the 21st century. The human race has endowed itself with a new source of energy, Divine Grace energy, and has embarked on space exploration with particularly remarkable economic development. As they extended their exploration to Pluto, an unidentified life form called Nergal suddenly attacked and destroyed the human colony. In order to combat this new threat, the United Ground Forces decide to use the "G's Frame", an ancient robotic weapon unearthed from ruins around the world and controlled by a group of young girls nicknamed "Ancient Girls"