There are many universes out there, an infinite number in fact each with a different origins. For some they arose naturally through events such as a big bang, or particles of other universes coming together to create a new one, but there also exists universes created artificially. Wither it be from ultra advanced alien races or by gods they were carefully crafted to the desires of its creator, desire being a very important word in some cases. With the wide variety of universes, advanced universe building races, and gods, there are of course quiet a few worlds the likes of which one would think only existed in porn (porn that someone in some random universe is probably writing).
This brings us to one of the many universes of Lustverse 149.085, one of the many multiverses where each universe revolves around lust. One of the deities that created many of these universes, Meljin, has recently gotten into a genre of Anime called Isekai spending many days on end wanking off to it. Suddenly they are struck with a brilliant idea and decided 'Why not do this myself?' First they started by creating a new universe specifically for that purpose, a generic fantasy setting with elves, dragons, magic, that stuff, and then they searched the many multiverses for someone to Isekai.
With the power at their disposal Meljin searched the cosmos, trying to find the perfect candidate. They knew they didn't want to take them from a Lustverse, because that would be to boring, but they also didn't want to send someone who couldn't enjoy this world at all. They needed a mortal that had all the same fetishes as themselves, they needed someone repressed enough they wouldn't immediately just throw off their clothes and start fucking, but they did have to be the type to eventually start doing this.
Finally Meljin found their perfect candidate, Alex, a mortal existing within one of the Earthverse's, one of those multiverses with a big focus on one planet called "Earth." Alex was perfect, they held all the same fetishes as Meljin, they had the same sexuality, and while like most of the mortals of their world Alex was not overly sexual, but they were still very open. With their perfect candidate chosen Meljin made sure to get permission from whatever god was in charge, who agreed rather easily, and while they slept transported Alex away.