Three computer-savvy kids, Naoto, Yuka and Ippei created their own videogame superhero, but then discover it possessed by an inter-dimensional police officer, Gridman. Pursuing an evil program called Kahn Digifer, he merges with Naoto and fights Kahn Digifer's digitized monsters (created by social misfit Takeshi) in order to prevent the computerized demon from wreaking havoc on the Human World.

All over the earth strange glowing objects in the form of letters in an unknown language appear in the skies. In order to investigate these strange phenomena, the Earth Defense Forces form the Science Guard Agency led by Captain Akiyama. Akiyama immediately forms a top rated team of scientific experts.