Twilight Sparkle has spent years as Discord's protege, studying the Magic of Chaos. But when rumors of a strange phenomenon dubbed "Friendship" show up in a small outlying town, the Emperor sends his star student to find out what's going on. Twilight goes with the best intentions and quickly discovers there is more than meets the eye going on in Ponyville...
Inspired by this post on r/mlpwritingprompts, by MetaSkipper. Original version by me is in the comments there.
Emperor Discord sends his star pupil Twilight Sparkle to investigate a mysterious new phenomenon called "Friendship".
After accepting the will of Chaos and remaining Discord's student, Twilight Sparkle returns to Ponyville to destroy the Tree of Harmony