Okay, so I've been poking around for this exact thing lately because I keep hitting the same walls. The big platforms like Tumblr and Pinterest are basically visual mood boards—you get these gorgeous, highly-styled graphics with a single evocative line, like 'Zenitsu finally works up the courage to hold your hand during a thunderstorm.' They're fantastic for a quick vibe check, but if you're trying to build out a full scenario with some meat on its bones, you often have to dig into the tags or the blogs that post them. The real gold, though, for me, has been on Twitter (or X, whatever).
There's a subset of writers there who do these mini-thread prompts. They'll start a thread with 'Demon Slayer Boyfriend HC: Tengen Uzui Edition' and then list out 5-7 bullet points that are way more specific. Things like 'How he'd react if you got hurt because he was showing off' or 'The absolutely ridiculous, over-the-top anniversary gift he'd plan that involves at least three unnecessary explosions.' The character voices in those snippets feel sharper to me, maybe because the format forces conciseness. You're not getting a full story, but you're getting a key character beat that you can unpack yourself.
I've also found that some of the best inspiration comes from completely outside the fandom. Reading a romance novel with a boastful but secretly insecure hero made me think, 'Wow, that's totally Inosuke's deal if you stripped away the boar head.' Or watching a drama where a stoic character slowly opens up—that's pure Giyuu fodder. I keep a separate note on my phone just for those cross-pollination ideas. It's less about finding a pre-written 'scenario' and more about training your brain to see the dynamics you love in other stories and then mentally recasting them with, say, Kyojuro Rengoku's specific brand of fiery enthusiasm.
The main thing I'd watch out for is the tone shift. A lot of the premade scenarios, especially on quote-video apps, lean super fluffy or straight-up suggestive. If you're aiming for something with more plot or a slow-burn tension that fits the darker 'Demon Slayer' world, you might have to Frankenstein a few ideas together or use the fluff as a starting point and then ask, 'But what if a Lower Moon attacked right now?' That's where your own spin comes in.