In 2025, mechanized beings known as Kikou abruptly emerged and assaulted humanity, wrecking countless cities entirely. Civilization collapsed into ruin, yet a fragment of a Kikou was later discovered in Japan. Consequently, the Tokyo Kikou Institute—Toukigen—was founded to study the Kikou's armaments. Embracing the adage 'fight poison with poison,' employing Kikou against Kikou became humanity's final strategy. Nine years thereafter, research yielded a new weapon called the Muttsu, nearly ready for battlefield deployment. The Muttsu, a formidable fusion of human ingenuity and robotics, was designed to counter the Kikou's overwhelming power. Its creators believed that only a pair of pilots could wield such a machine. Two pilots—boy Rin Sagami and girl Yuzuru Midou—were selected to command the Muttsu, carrying society's aspirations into battle. They confront their mission with valor, yet a harsh destiny lies ahead for them.
