A sudden, extreme monster apocalypse, thousands of humans across nearly every continent contracted a mysterious disease transmitted by giant, dangerous, man-eating monsters. Except for those in the Western and Southeastern Continents, who managed to survive. Children also fought in succession during the great war of the Monster world to defend the Continents.

It is known that there are three organizations on both continents: -The Battle of Mankind, Intelligentia Association. -Combat (Children) Society, led by Experimentalis Scientificalis. -Research subjects Human-Monster, Experimentalis Scientificalis, led by Intelligentia Association.