When the Sonic Rainboom inspired Twilight Sparkle to pass her entrance exam, Princess Celestia knew that this was the one, the final element of Harmony, the filly prophecied to save her, and her sister, and the world from certain doom.

Princess Celestia made a terrible mistake.

She never even knew about the most magical unicorn in all of Equestria, because that filly was far away from Equestria, in a place where few ponies dared to tread. For Twilight Sparkle, the Sonic Rainboom was the greatest moment of her life, but for this filly, who was to become the world's only hope, it was the worst.