Twilight Sparkle has turned evil and is bent on taking over Equestria for herself; she has already killed Applejack, Rarity, Rainbow Dash and Princess Celestia, stealing the Elements of Harmony, using their raw power to destroy anyone who stands against her path to total domination. Pinkie Pie and Flutterhsy evading Twilight's pursuit, with their respective Elements of Harmony in hand, Twilight enlisted Discord to draw out the two remaining elements by turning all of Equestria into a post-apocalyptic wasteland, and when that didn't work she released all foes she had previously defeated, including the likes of Queen Chrysalis, The Dazzlings, and Lord Tirek.
Sunset Shimmer, a former student of Celestia's, now works as a smuggler for anyone with good enough cash, all while avoiding rival employers and Twilight's Royal Guards, dubbed "The Alliance" by her and other smugglers.
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Inspired by works such as: Star Wars, Firefly, and Fallout
Art by bakki
Edit (2/10/18): Revised almost everything, up to chapter 7 and the title.
Edit (5/31/21 - now): edited for better, more consistent terminology, word choice and other cringey things.