Where To Find Undertale Crossover Fanfiction?

If you're searching for that specific crossover niche, AO3's tagging system is your best friend. I'd start by combining the 'Undertale' fandom tag with the 'Chara (Undertale)' and 'Frisk (Undertale)' character tags, then use the 'Crossover' filter. It's a bit of a process, but you can save the search. Honestly, the quality varies wildly; some authors get the eerie, introspective tone of those characters perfect, while others just slot them into another universe without much thought. I found a surprisingly good one where Frisk and Chara were ISOs in the 'Tron: Legacy' grid, which shouldn't have worked but somehow did. Sometimes, though, the platform-specific archives for the other franchise in the crossover yield better results. If you're into, say, a 'Deltarune' or 'OMORI' crossover, searching those smaller communities might surface stories that haven't been cross-posted to the big archives. The hunt is half the fun, even if you wade through a lot of forgettable stuff to find the one that clicks.