I want to make one thing completely clear at the start:
This is FanOfMostEverything's fault.
I usually have one mobile game which I can play in waiting rooms. (Assuming those open up again any time soon.) This used to be Marvel Puzzle Quest, but following the loss of game progress with a tablet switch, it became Hogwarts Mystery. As it turned out, my tweets on the topic somehow talked Georg into playing, and I put together a minor game guide to ease what I was expecting as his pain.
The game has Friendship Events: stages during which you're supposed to strengthen your bond with other students. And one sidequest requires you -- quoting myself here -- " to get as close to Bill Weasley as anyone who isn't named Fleur."
FOME quickly cracked that it had taken him a moment to realize this wasn't an unexpected crossover.
...hello, plot bunny.
So here it is. An unexpected crossover, all 12k of it. And the scariest thing? Aside from my utter bone-crushing exhaustion, it didn't feel like 12k. I've never tried writing anything HP before, and it just felt so... natural. Not as if I had always possessed a story waiting to get out -- this one was pretty much born in a single day -- but like I'd been walking the halls for so long as to have no problem in finding my way.
And then there was a perfect title.
Human/pony/Major Franchise one-shot crossover with no Romance tag. Here come the downvotes!