SunsetSparkle

SunsetSparkle is the femslash ship between Sunset Shimmer and Twilight Sparkle from the My Little Pony fandom.

Equestria Girls
The newly crownded Princess Twilight arrived at the castle in the Crystal Empire for a princess summit. She is uncomfortable with her new statis and her new wings. She tries to sleep and eventually suceeds. But, a mysterious mare steals her crown and runs off into a mirror. Princess Celestia reveals that it was her fomer student, Sunset Shimmer. She tasks Twilight to go into the mirror world to get back her crown (since it's also the most powerful Element of Harmony). Twilight and Spike goes to the mirror world. There, they realizes that they have been turn into a human and a dog respectively. Twilight ends up meeting Sunset after wandering into the Canterlot High School. The latter was bullying a human Fluttershy. Twilight interrupts her and Sunset doesn't recognizes the princess. She talks down to her, saying that since she's new she shouldn't confront her.

Fanon
This shipping started mostly after Sunset's redemption. But because Princess Twilight started to not appear in the EG universe, fans quickly moved over to SciTwiShimmer.

Fan Fiction
Sunset/Twilight on FanFiction.Net

Sunset Shimmer/Twilight Sparkle (My Little Pony: Friendship is Magic) on AO3

Trivia

 * Sunset's name is meant to evocate the same vibes as Twilight's name. (Starlight's name is also based on that principle.)
 * Following the above, both names are different times of the day.

Variations
SciTwiShimmer refers to the ship between human Twilight Sparkle and Sunset Shimmer