Alright, so you’re looking for Shun x Mio crossovers. Honestly, that’s a pretty specific and kinda niche corner of the 'Dance Dance Danseur' and... wait, I’m assuming you mean Mio from 'Kimi ni Todoke'? That’s the most common one I’ve seen. If it’s another Mio, this might be off, but I’ll run with it. The main thing is, these two characters exist in totally different tonal universes—one’s a ballet prodigy, the other’s a sweet, shy girl—so the writers who do tackle it are usually creating whole new worlds to make them meet. It’s less about finding tons of fics and more about finding the few that really nail that weird, compelling dynamic.
You’re not gonna get a simple answer like ‘Archive of Our Own, filter these tags.’ The crossover tag itself is barely used consistently. I’d start on AO3, absolutely, but you gotta be crafty. Search individually for ‘Shun Sarashina’ and ‘Mio Akiyama’ (from ‘K-On!’) or ‘Mio Kanzaki’ (from ‘The Idolm@ster’), because sometimes the tags are a mess. Filter by English, sort by kudos, and maybe even check the ‘Other Media Fandom’ tag. Wattpad has some, but the quality is a total gamble; you’ll find a lot of high school AUs that mash them together without much thought. I remember one story that put them in a generic coffee shop and it just felt… off. The good ones, though, really dig into Shun’s intensity and how it might clash or mesh with a softer, gentler Mio’s worldview.
Don’t ignore smaller forums or even Tumblr. I stumbled on a fantastic, unfinished piece years ago on a now-dead blog that explored Shun teaching Mio how to move with more confidence, using ballet as a metaphor for her coming out of her shell. It was beautiful, and I’ve never been able to find it again. That’s the tragedy of niche crossovers—the gems are often hidden in places you don’t think to look and can vanish overnight. My advice is to follow authors who write good Shun-centric gen fics; sometimes they dabble in crossovers as side projects.