In the year 2010, mankind discovered he was not alone in the universe.
A new landmass called Equestria had materialized in the Pacific Ocean, introducing humanity to ponykind. However, the landmass' arrival had an unintended side effect. The leylines that had laid dormant under the surface had started to awaken, spreading magic all across the Earth. And due to humanity's lack of contact with magic, the energies emerging from the leylines were harmful to humans. A solution was soon created in the form of a potion that would convert humans into the various races that inhabited Equestria.
Not many were willing to change however, but near the end of the decade, a new version of the potion was created: One that would allow humans to keep their bodies, while making them immune to magical energies emerging from the awakened leylines, and also allowing them to use magic.
This new potion was called the 'Transhuman Potion'.
These are the stories of those who took the 'Transhuman Potion' variants.
Edit: Now has a TvTropes Page: http://tvtropes.org/pmwiki/pmwiki.php/Fanfic/TheConversionBureauTranshumanism