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Pokemon is set on the Venusian colony.
The terraforming of Venus started with megabacterial colonies, referred to by their creators as "The Grime." They were extremophiles, able to survive and indeed to thrive under the harsh conditions on Venus.
The orbiting station monitored the progress and sent additional artificial animals to cleanse the atmosphere ("Haunts" and "Koffings"). Eventually, it was easier to make an artificial faunosphere than to import Earth animals. Most of the colonists were already familiar with the "pocket monsters" already anyway.
And then, the great psychic disaster happened. All the Unown and Mew of the world, which had until that point been controlling the populace, gave Venusian humanity a collective amnesia. At the same time, a team of Clefairies / Clefables took over the space station.
There were hints that their reality was psychically contructed. Why were only 150 known in Kanto, yet a global communications system existed? Why are the towns so small?
Only Team Rocket has some pieces of the puzzle, and they've spent millions to figure out how to get humanity's rightful place back.
On top.