Finding the real gems for that pairing means knowing where different kinds of writers tend to settle. AO3 is basically the flagship for any character dynamic with serious thematic weight, and Diavolo and Lucifer from 'Obey Me!' definitely have that. Writers there dig into the power dynamics, the political maneuvering, the whole 'two rulers' thing in a way that feels intentional. I found this one series that treated the Devildom like a proper court intrigue drama and it just clicked. The tagging system means you can filter out the fluff if you want that heavier stuff.
Discord servers are a different ecosystem. You get quicker updates, more spontaneous 'what if' scenarios, and sometimes rougher drafts that have this raw energy you don't get in polished works. I've seen a few authors there who post snippets that are all about their playful, competitive banter, which is a fun contrast to AO3's epic sagas. It's less about finding a finished masterpiece and more about catching the process, which has its own appeal.
Tumblr is hit or miss now, but the hits are atmospheric. You'll find moodboards and shorter, poetic pieces that focus on a single moment—a shared glance, a private conversation away from the council. It's where the aesthetic of their pairing gets highlighted. Wattpad, honestly, I steer clear for this specific crossover; the tone usually skews too young for the complexity I think those characters deserve.