Can't believe I'm the first one here but this is my jam. Honestly, for Bakugou/Kirishima stuff that's actually spicy, you gotta hit Archive of Our Own and filter like your life depends on it. Sort by kudos and then filter for the 'Explicit' rating, that's the baseline. But the real trick is finding writers who get the dynamic right—the ones who nail Katsuki's aggression turned into something else and Eijirou's unwavering loyalty that's got its own fierce edge. I've wasted hours on fics where the spice feels generic, slapped onto any pairing. The good ones weave it into the fabric of their rivalry-friendship-whatever; it's all about that push-pull, the vulnerability Bakugou would absolutely hate showing and Kirishima being the only one stubborn enough to wait for it.
I'd also lurk on specific Tumblr blogs. A lot of writers post snippets or links there before cross-posting. Search tags like 'bkdk' no wait, that's the other one, I mean 'bakushima' or 'kiribaku' and 'nsfw'. The tagging system on AO3 is your best friend, but sometimes the absolute gems are hiding in 'M' rated fics that are basically Explicit but the author was being coy. Also, don't sleep on the 'aftercare' tag if you want the spice to have some emotional payoff, which, for this ship, feels essential. Otherwise it just feels like two angry blobs going at it. My personal bookmarks are full of fics where they're pro heroes sharing an apartment and the tension finally snaps after a brutal fight. That scenario never gets old for them.