Every action has consequences, no matter the intent. To clear her slate, Twilight Sparkle will go to any lengths to settle the score with Celestia, even if it means a fool's errand to a land ravaged by chaos.
Rarity liked the tale of The Four Princesses as a filly, even if she knew it wasn't real. Princesses fighting against a spirit of chaos? A library under a tree? Please. But then she grew up and found out some bedtimes stories were quite real.
I have only one purpose in my life now. Its to keep her safe, at any cost if that's what it takes. I will protect her more than SHE ever did for me. I will not let her down like SHE did to me. My name is E...Esdeath. And all I have left is Cadence