Through the moist, pitch-black darkness the eerie sounds of giant machinery can be heard. In an advanced facility that has been invaded by otherworldly beasts and local inhabitants, the fully-automatic system controlled by the main computer is still operating like a mad man. Awakening inside an abandoned laboratory, the green, ambiguous lifeform MO discovers that it not only has to face an extremely hostile and sinister environment, but it also must face humans who, having been taken over by alien parasitic plants, are now stuck in the endless limbo between death and rebirth. What's more, there seems to be an eerie presence that's watching all of this from the shadows. After groping around for clues, MO gradually becomes aware that it is responsible for a mission of immense importance. Under the guidance of the mysterious mutterings in its ear, MO is able to overcome one obstacle after another.

Who caused this disaster? And on this path that leads to answers for every unsolved riddle, what sorts of trials and tribulations lie ahead?