Honestly, my first stop would always be Archive of Our Own, no contest. The tagging system is a lifesaver for digging through specific dynamics, and you can sort by kudos which usually surfaces the stuff that really resonated with the community. Wattpad has a massive volume, obviously, but the quality can be super hit-or-miss; it’s more for casual browsing when you’re just in the mood for something quick and trope-y. I’ve found some surprisingly decent fics on FanFiction.net by sorting by favorites, even though the interface feels a bit dated.
A lot of the really passionate, character-deep dives I’ve stumbled across were actually on Tumblr, though. Writers will post threadfics or multi-part stories there, and the reblog chains help them spread. It’s less of a centralized collection and more of a scavenger hunt, but that’s part of the charm for me. Sometimes you’ll find a gem linked from a Discord server, too, but those are harder to just wander into.
What’s funny is that the popularity seems to shift with whichever YouTuber is playing the game at the moment. A new playthrough series drops, and suddenly my AO3 bookmarks explode with new Ayano/Kokona stuff I have to catch up on. The fansites and wikis sometimes have story sections, but they’re usually not as active as the big archives.