Denkou Choujin Gridman (1993)

Three computer-savvy kids, Naoto, Yuka and Ippei create their own videogame super-hero, 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.