Three quarters of the world is now barren wasteland. The other fourth is soon to follow. The Earth has been invaded by an unknown species called "phantoms." Humans have been creating androids and advanced weaponry to fight off the phantoms. Many different kinds of androids have been designed, from housekeeping androids to mercenary androids. Iris is an advanced mercenary android that can kill 6000 phantoms in a mere 2 minutes. Nagi Ichizaki Zyr finds her in a junkyard one day and he decides to take her home and repair her, without knowing that she is the hope of the world.

adapted from the light novel series of the same name