Throughout the Plazma Burst series, either Earth or another human organization has been at the peril of an alien race of some sort. The first alien threat consisted of the Falkoks. These enemies were stationed on an unknown planet in the first installment. Then there were the Usurpation Forces, seen attacking Earth in the second game for an unknown reason, possibly to enslave the human race. The Falkoks are seen in the first game on a planet that is not Earth, but is a close neighbor to Earth. It is not known if this race is the native inhabitant of the planet, or just a visitor, sent to fight the human soldiers.
The Usurpation Forces are a high-tech race, that fights the Civil Security as well as the Marine on many occasions, intent on taking over Earth. They were discovered by accident when humans first invented teleportation by an experiement. They use the Alien Pistol, Alien Rifle, and the Alien Shotgun, as well as other weaponry. Here are the known types of Usurpation units.
- Minor Usurpation Soldier - The lowest rank which also has the lowest health.
- Major Usurpation Soldier - Higher rank than the Minor, and has more health.
- Advanced Usurpation Soldier - More health than the Major, but by a small amount.
- Usurpation Destroyer - Highest rank and also has the highest health. This unit also has slower movement speed than the other ranks but carries a heavy weapon set.
The Falkoks are another species of aliens seen guarding their planet in Plazma Burst: Forward to the Past. Not much else is known about this species. Currently, only two known Falkok units are in the series and consists of: