Rainbows After Rainby Nitro Indigo
A long time ago, Equestria was the most prosperous nation in the world. Princess Twilight Sparkle's reign was an age of harmony where creatures of all shapes and sizes co-existed. But then, one day, the ponies all disappeared, and so did magic.
In a centuries that followed, the creatures all went their separate ways, but a young changeling named Solifuge dreams of recreating Twilight's utopia. When a kirin named Moonbow Shine crashes her hive's anniversary festival, she's the only changeling willing to talk to her, and together they set on an adventure that will uncover the secrets of the past...
Or, My Little Pony: A New Generation AU where the Earth ponies are changelings, the unicorns are kirin, and the pegasi are hippogriffs. Inspired by this art by Scribbling Potato. Cover by Little Tigress.
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Come back later when there's something to read.
Having preread this, this is a solid start with some clever swaps. You did well depicting the changes in a natural way.