This is a Fallout: Equestria and Harry Potter Crossover, inspired by Harry Potter and the Crystal Empire for those curious.

~~~~~~~~~~~~~~~
What if, in the battle against Quirrel, Harry accidentally smashed the Philosopher's Stone on the man's head? What if this transported the entire school, along with all of the lands belonging to it, into the Post-Apocalyptic Wasteland of Equestria?
And what if all of the students, teachers and Ghosts got ponified in the process? Well, Harry has some other problems to boot, like figuring out what to do in this new world, and managing as both a Alicorn, a female at that, and one of six no less, as well as trying to keep the school and his friends safe.

~~~~~~~~~~~~~~~
So, we're above 100k in length, I'm pretty proud now :D
Average chapter length so far is 4934.9545454545 as of chapter 22

It is the year 0179 of the Cloud Century. Almost two centuries have passed since the Pegasus Enclave closed the sky and cut off the toxic, uninhabitable surface world. A new home for ponykind, where pegasus ponies are born, and raised, and die.

Before the war, before the sky was cut off, something terrible was locked away. Chamomile is an average pegasus, born into a family of archaeologists and living at the edge of Enclave territory, far to the north. When she stumbles into ancient dangers and conspiracies, she finds her quiet life turned into a horror story. Can she set things right, or is the Enclave doomed?

A Fallout: Equestria sidestory. Thank you to all my readers, patreons, and well-wishers!

As always, I most look forward to seeing what references and cameos people notice. You surprise me sometimes with how you pick up on minor details!

Here's a gallery of the previous cover art, as well as a few bits of character design I put together: Gallery