Resident Evil's Chris Redfield and Jill Valentine have one of those partnerships that's just begging for deeper exploration, and fanfiction spaces are where that happens. You'll find them everywhere, but the density and culture differ.
Archive of Our Own, AO3 for short, is the undisputed heavyweight for polished, tagged, and often novel-length works. The tagging system is a lifesaver for finding specific tropes—whether you want post-'Resident Evil 5' angst, 'Resident Evil 1' mansion-era tension, or modern domestic fluff. The quality there tends to be higher on average, with some authors who really dig into their shared trauma and mutual protectiveness.
For more casual, quick-fire updates and a community feel, FanFiction.net still has a massive, if older, archive. The search is clunkier, but there's a trove of classics from the mid-2000s you won't find elsewhere. Tumblr is less a host and more a network; you'll find snippets, headcanons, and mood boards that lead you to stories on AO3 or Google Docs. It's the social heart of the ship for a lot of people. Discord servers are the real hidden gems—tight-knit groups sharing WIPs, brainstorming, and diving deep into character analysis you rarely see on public platforms.