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The Unknown (as the name implies) are an unknown alien race and monstruos living beings that are the possibly the main antagonists of the light novel and anime series Qualidea Code.
The Unknowns are responsables for the dawnfall of humanity. Their origin is unknown since they came from another dimension and caused several attacks in mass around the Earth, but is indicated that they are machines or some kind of bio-machine controlled by beings from another dimension and is clearly seen that they are not organic. Unknowns are opponents faced by the resistence of humanity. The print spin-offs put forward the idea that they are an alien menace, and what's more are utterly hostile to humanity as a whole, attacking the world killing every life form.
Despite being responsible for the fall of humanity, it is theorized that they are possibly trying to free humans from some of mental control in an illusory world created by the military. It is also theorized that some of them are humans who have been killed in the illusory world and are free from the mind control.
The Unknowns have several type of forms, some of them can have the appearance of spaceships, towers, humanoid beings, dolls, robots, fighters, star fighters and many others.