The Nemesis are the villainous force from Metal Black.
In the year 2042 a star appeared near the planet Jupiter, propelling asteroids towards Earth. The damage was severe, but soon after started an invasion by an alien race which was named the Nemesis. With little resistance, they successfully take over our planet, intending to plunder our planet of inorganic materials they needed to survive.
Strange molecules started littering the planet, the same ones which were used by the Nemesis weaponry. Scientists study these molecules, calling them "Newalone", thus starting "Project Metal Black" to create a fleet of spacecraft capable of using the same weaponry as the invaders. The spacecraft was named CF-345 Black Fly. However, Earth passes a surrender treat to the aliens, promising to withdraw all of Earth's defense forces, which also applied to Project Metal Black. This obviously led to shortage of natural resources and a severe drop on the planet's population.
It was not long before someone discovered about Project Metal Black. An unknown person found the hangar where the Black Ray were stored, deciding to pilot the ship and fight the Nemesis by himself. He manages to defeat the Nemesis forces on Earth, traveling after the Nemesis homeworld, the star which had appeared near Jupiter. He finally destroy their leader and their homeworld in the proccess, apparently dying as well.