Five years ago an accident released microscopic machines called nanites into the atmosphere which infected nearly every living thing on Earth. These nanites can randomly activate and usually mutate the host into a berserk monster, called an EVO (Exponentially Variegated Organism). The organization known as Providence was formed to fight these EVOs worldwide. And their secret weapon is Rex, a teenage EVO who can control the nanites in his body to form various biomechanical appendages to fight other EVOs and even cure some of them by deactivating their nanites.