Fanfic:Sunshadow
 
“In a show of compassion Celestia took a homeless filly into her care, and because of her talent for conjuring fire she became the princess’s first student in a very long time. Over the years, her pride and hunger for power worried the monarch greatly, but those concerns were answered by the arrival of Twilight Sparkle, whose mere presence roused Sunset Shimmer’s empathetic soul from its slumber.
 
“Eighteen years have passed since that first day, and the unicorn has finished her magical studies to move on to greater things. She’s haughty and ambitious, but grounded by her fellow student (and their little dragon). Her greatest desire right now is to help Twilight open up and stop hating herself for things she can’t change… which would be easier if she didn’t look down on everypony else.”