Fanfic and sex go hand in hand since Amok Time, but there isn't a lot of work on how it's represented there. This study took a look at that, specifically examining aggression, which turned out to be quite prevalent.
(Also, full credit to the first author, Ezelbahar Metin, for getting "reading erotic fanfic" to be part of their PhD work. I'm envious)
Link: https://link.springer.com/article/10.1007/s10508-026-03523-0