WARS is set in the future of our solar system. Three factions are at war: Earth, Gongen, and the Mavericks. Earth is capitalistic and militaristic with bases on Luna and Venus. The Gongen are actually Asians that were forced to migrate to Mars because of a nuclear catastrophe. They declared independence and renamed the planet to Gongen. The Mavericks are basically a very loose affiliation of opportunistic cyber-gangs that inhabit the outer rim of the solar system (i.e., moons of Jupiter and the asteroid belt).
Enter the Quay and the Shi:
The Quay were a slave race that retaliated against their former masters, the Shi, by destroying the sun of the Shi's homeworld, Seyal. The Shi prevented the destruction of Seyal by creating a rift in space that allowed their planet to enter into our solar system. Hordes of Quay also came through the rift aboard their life ships.
The Shi and Quay are hard to describe, but here goes:
The Shi are a telepathic race with a superiority complex. They have no legs, and they actually float. Their faces and bodies kind of resemble the Creature from the Black Lagoon to me.
The Quay are a savage, predatory race. Their bodies are insect-like with multiple legs and two arms on a long torso. Their faces have a demonic appearance.
Amid the conflict between these five factions, there is one more twist:
The rift that the Shi have opened is emitting some sort of energy. Apparently, some people (and aliens) that are exposed to this energy have changed. The change varies from person to person (or from alien to alien). If you consider all of the different mutants from the X-Men (movie or comic), then you'll get the idea. The mutated people and aliens are called kizen though, not mutants.
Player characters in the WARS RPG are kizen, usually from one of the human factions. There are rules for playing a Shi or Quay in the "Battlefront" supplement, though.
Hope I helped.