The Earth Alliance fleet will do its utmost to challenge the space life form Nergal, which destroys everything related to the wisdom and Divine Grace system of humankind. As humanity continues to lose, the last hope was a girl with a variant who could manipulate the ancient robot weapon "G's Frame" excavated from archaeological sites around the world. The main character, Reika Minamimiya, goes to the pilot selection test of the AG unit without telling her parents, along with her friend Misaki, in order to find her sister, Rei Ame, who belongs to the 1st AG unit that went missing in the battle with Nergal. On the way home from the exam, the girls attacked by Nergal--!