Look, AO3 is basically the main hub for that sort of thing and it's not even close. The tagging system over there is a lifesaver for finding exactly what you want—you can filter for the pairing (Midoriya Izuku/Todoroki Shouto), the specific trope if you're after something like 'First Kiss' or 'Accidental Kiss', and even exclude stuff you hate. Wattpad has a ton too, but the quality can be super hit-or-miss; you really have to dig through the amateur hour stuff to find the gems. Sometimes you'll find some decent threads on dedicated 'My Hero Academia' forums or on Quotev, but those feel kinda... dormant now. Honestly, if a fic isn't on AO3, I probably haven't read it.
A weird spot I stumbled onto some good ones was actually on Tumblr? Writers will sometimes post short drabbles or snippets there with tags, and if you follow the right blogs, they'll link to their full works on AO3 or even Google Docs. It's a bit more of a scavenger hunt, but it feels more community-driven. Fanfiction.net still has a massive backlog, but the tagging is a nightmare and the culture there has shifted so much. For Tododeku specifically, AO3's where the committed writers and readers have settled.