Yuletide Guessing Game

This is being done by various other people, and I thought I would give a go of it this year. If you can guess which story I wrote for this year's Yuletide from all the ones in the archive (and you didn't beta read for it--but hey, I changed the title after the last of the editing was complete) then I will write a drabble for you in that fandom.

There's a chance it would become more than 100-200 words. Prompt of your choice.

Your only clue if you haven't read the locked posts is the icon I'm using.