Title: Same As It Never Was

Main characters:Twilight Sparkle, Princess Cadence, Princess Celestia, Sunset Shimmer, Princess Luna, Trixie, Queen Chrysalis.

Genre: Alternate Universe, Dark, Adventure, Romance, Slice of Life.

Pairing: TwilightXCadence, SunsetXCelestia, TrixieXLuna.

Canonical Placement: After A Canterlot Wedding.

Premise:
After the Changeling invasion, Celestia looks over the damage, death and destruction in cause, lamenting over the fact that she let her subjects down by not only being fooled by by the Chrysalis, but beaten by her as well. Twilight finds her and attempts to comfort her, but she leaves.

Later on however, she makes her way to the Canterlot library, specifically the Star Swirl the Bearded wing. There she finds a spell that can temporarily send a pony back in time (the same one Twilight used in “It’s about time” However, due to the fact that Twilight didn’t put in the right amount of magic, she ended up creating a stable time loop instead).

She uses the spell in an attempt to stop the invasion before it happened, however she is attacked by a mysterious figure in the process, causing her to use too much magic. As a result, she ends up sending herself back to a week before Luna became Nightmare Moon.

Seeing a different opportunity, she spends more time with her sister and even creates a holiday centered around her Moon (ironically on the day she was supposed to be banished).

When she is pulled back to her own time, she sees that much to her surprise, Sunset Shimmer is still her student, and the other changes to her timeline are made horribly clear soon after:

Luna rules over her Kingdom in Ponyville with her own student, Trixie.

Cadence ended up taking Twilight as her student and now rules over the Crystal Empire.

Canterlot, Ponyville, and the Crystal Empire are in a three-way war.

Celestia must now find out why things have turned out this way, and bring balance back to Equestria before their war tears it apart, but what part does a certain Changeling Queen play in all of this?