In a parallel world that resembles modern Japan, alien lifeforms known as "Muttsu" (Trick) fell from the sky in 2025 and wiped out many cities. Nine years later, pilot Yuzuru Midō, and her assistant, Rin Sagami, use a mecha made out of an enemy's remains discovered in Japan. However, battle causes memory loss for the pilot, and they must unravel the mystery as to why.