MO: Astray is a side-scrolling action-adventure platformer with puzzle elements. Through the pitch-damp darkness, the eerie sounds of giant machines can be heard. In an advanced facility that has been invaded by otherworldly beasts and local residents, the fully automatic system controlled by the main computer is still working like crazy. Waking up in an abandoned laboratory, the green, ambiguous life form MO finds that she must not only face an extremely hostile and sinister environment, but also humans who, having been captured by alien parasitic plants, are now stuck in an endless limbo between death and rebirth. Moreover, there seems to be an eerie presence that is watching all this from the shadows. Groping for clues, the MO gradually realizes that he is responsible for an extremely important mission.