When one fateful search through the Everfree Forest leads Rarity to a secret library inhabited by the spirit of an ancient alicorn princess, she realises that it may be time to start believing in fairy tales.
As an ancient alicorn trapped inside a library, Princess Twilight spent many a century dreaming of being rescued from her prison. Now, finding herself in an entirely new Equestria, she realizes she'd never planned for somepony to actually succeed...
Twilight Sparkle’s brilliant mind was gone, burned away by her own power when she nearly destroyed Canterlot twelve years ago. Now there is a monster prowling the Everfree. And it is starting to remember what true power felt like.
It has been almost a century since Twilight and her friends had discovered their destiny, and Celestia has been wracked with constant regret over the fate she has condemned her friends to. Luna looks to those very ponies to help Celestia smile again.
Twilight Sparkle is embarking on a new path in her life, and Luna is there to guide her to the right one. At long last, it is time for the Stars to come home.
Monster finds problems fitting in and getting used to her new world in Ponyville. To help adjust, she reaches out to Princess Luna who has many of the same problems now that she is recovering from being Nightmare Moon.
Congratulations, Twilight. With the Princesses on vacation, you're in charge of Equestria. Perhaps it's a bit early to congratulate you. After all, whether it's a jealous nobility or an unhappy military, your reign will be anything but
Luna's has enough to deal with as Princess Twilight's student. Between nightly nightmares of moon princesses and the threat of an old enemy returning from Equestria's past, Luna isn't going to be getting any sleep any time soon
Celestia decides to attempt to reform Discord, so she taps a pony with a similar background for the job. ("Keep Calm and Flutter On" as it occurs in the Petriculture AU.)
Twenty years before the Elements of harmony, before Nightmare Moon's Return, Celestia started a whole new slew of problems and headaches for herself and the ones around her. Thankfully Cadence doesn't mind foalsitting.
After a week of recovering from her return Princess Luna seeks to return what was lost by her banishment and find the one pony she cares for the most... her daughter.