The Earth Defense Force, a unified multinational military sponsored by nearly every country, is founded after detecting an impending alien visit in case the aliens prove to be hostile. In the year 2017, that proved to be true and the EDF fought against the Ravagers, an alien race that attacked Earth with giant insect-like creatures, UFOs, robots and gigantic, 120-foot-tall lizard-like creatures.

The EDF defends a fictional city called New Detroit against an alien invasion, aided by bio-engineered terrestrial insects. The Player goes by the name of ‘Lightning Alpha’, leader of an elite team of fighters, known as “Strike Force Lightning.” Along with two squad mates, Lightning is (usually) aided by local EDF fighting forces in the area, though they are poor compared to Lightning.