No character tag for poor Misty Fly!? Oh well…
The lands of Equestria are in ruins, destroyed by mysterious, billowing monsters who devour ponies. Some kind of cursed magic? Nopony knows.
The survivors forge on up in Cloudsdale, and only the re-militarized Wonderbolts go below and only for strategic, tautly planned, rigorously overseen missions. That is, until one day when Misty Fly gets it in mind to surprise her girlfriend, Lyra, with a special gift, and Soarin agrees to be her wingpony.
Same AU as my stories Happy Birthday, Sugarcube and Planted in the Clouds (it would be during the 5th chapter of Planted). All can be read and understood separately but reading all three will add more context and details to the AU.