>>39485811Generally, fetishism derives from a separate desire. Like maybe wanting to have sex with a Goodra is due to someone liking wet sex with an overweight girl? Wanting to have sex with n Eevee might be due to either a latent bestiality desire, or because someone is misinterpreting a love for a dog (non sexual) with their personal obsession with sex (non bestial).
I think I recall reading the reason why foot fetishes exist is because the part of our brain that takes in info from foot stimulation (tickling, etc) is neighboring the part of our brain which handles sexual desire, so the signals get crossed.
Honestly? I think each individual person has a long history of weird sexual and nonsexual events which manifests in the form of sexual desire. Sometimes, that desire makes you want to fuck a Pokemon.