Finding Korean romance fanfic depends on what kind of 'hot' you're after. If you mean steamy, romance-driven K-drama or K-pop fanfiction, Archive of Our Own is probably the biggest hub. The tagging system is your best friend there—search for your favorite Korean actor's name, a drama like 'Crash Landing on You', or a K-pop group tag, then filter for the 'Explicit' rating. Wattpad also has a massive amount, but the quality can be super hit-or-miss; you really have to dig through a lot of cliché-ridden stuff to find the gems. Sometimes it's more fun to lurk in specific fandom spaces on Twitter or Discord, where people share links to their Google Docs for racier stuff that might not be on the main platforms.
Honestly, a lot of the most intense, novel-length Korean romance fanfic I've stumbled upon was actually originally written in Korean on sites like Naver Blog or Fan Cafe, and then translated by dedicated fans. If you're willing to deal with machine translation or wait for updates, that's a whole other world. The tropes and pacing can feel different from Western fanfic, which is part of the appeal.