Soon after a shuttle returning from Mars burns up on re-entry, monstrous creatures called Ancients begin appearing across Tokyo, immune to ordinary weapons. Takeru Hinata, a teenager with a troubled past, is one of the few whose body can bear the experimental MARS suit built to fight them, fielded by the all-female combat agency AAST. This short OVA strings together the animated scenes of the game it adapts as Takeru and the agents take the Ancients on.