Today was a very special day. Celestia had been reading the Threads of Time, and she had determined that today would change the course of history forever. Today was also Academy Entrance Exam Day, but she knew that was only a small part of it. There were six great Threads that were all conjoined by one critical event. Never in her lifetime had she seen something so important. She had all six names memorized: Applejack, Fluttershy, Pinkie Pie, Rainbow Dash, Rarity... and Twilight Sparkle. They all had their part to play, and so did she. Like a nervous actor, she waited offstage for her oncoming cue.
There! Right on time. Celestia heard the explosion just outside in the courtyard. She looked up and saw something she hadn't witnessed in years: the Sonic Rainboom. "Rainbow Dash," she murmured. After that, like clockwork. 3... 2... 1... The tower just above her echoed in a great reverberation of magic. Lightning fanned out in all directions, and the air filled with the sharp taste of ozone. Only she could stop the power overload now taking place. Up the stairs she ran, four by four, until she found the room. There, the little filly, wracked with magical spasms, and the observers, held within her telekinetic grip. She did as the story demanded: she placed one hoof on the filly's shoulder, and the magic receded. Now she could recognize the pony who would face all of--
"Who are you?!" Princess Celestia asked.
"What do you mean?" said the filly.
"Where is Twilight Sparkle?" she asked.
"S-she's after me, Princess. I'm Rarity, Your Highness."
"But... I didn't know you had so much magical potential!" Celestia told her.
"I didn't think so either, Your Highness. But when that explosion happened, I-I panicked! It just came to me!" Rarity replied.
"Well, stay here for a moment. You certainly have the ability to be my protegee, but--"
"I would be the protegee of Princess Celestia? That sounds wonderful!"
"H-hold on. I need to see what Miss Sparkle can do."
"As you wish, Your Majesty," Rarity said. Together, they went down to the waiting room, where the little lavender filly and her two parents sat anxiously by the door.
When the two of them appeared in the door, Twilight jumped up and asked, "What was that? Some kind of bomb?"
"Only a pegasus stunt, my dear," Celestia said. "Nothing so dangerous." She looked at Twilight's flank, but her cutie mark had yet to appear. "Would you please come with me, Miss Sparkle? It's time for your test."
"Oh. Okay..." Celestia could see that the poor girl was a nervous wreck. Was this really who fate had chosen as the student of friendship?she looked to Rarity, who carried herself with grace and propriety. Twilight apparently looked too, because she piped up, "Hey! You've got your cutie mark!"
Rarity looked back. "So you're right. How marvelous!" The three diamonds seemed to sparkle in the morning sun. Seeing Twilight's somber face, Rarity added, "I bet you're going to get yours as well soon!"
"Thanks! That's so generous of you." After that, they walked silently to the main chamber.
The first thing they saw was a little dragonling crawling about the floor. Rarity picked him up with a happy jump. "He's so adorable!" she cooed. "Such a spiky little head. I'm going to name him Spike."
"Very well, Rarity. Please stand to the side." Celestia turned to the examiners. "What do we have for Twilight Sparkle?" she asked.
"That was our last dragon egg, Your Majesty," said Prime Factor.
"We do have a thaumoprism, Princess," said Glowlight.
"Perfect!" Celestia said. She magicked it from Glowlight's hoof to Twilight's, then told her, "All you need to do is match your magical frequency to the lines on the prism. If you do that, you'll get eight colors through the prism. Do you understand?"
"I think so," twilight said. After Celestia set the prism down, Twilight began pulling her magic from deep within. Strangely, Twilight couldn't even get a consistent beam created; it wavered and flickered weakly. Celestia couldn't tell if Twilight was using her magic wrong or if there simply wasn't anything more to draw. "Don't strain," said Celestia. "Let the magic move through you naturally."
"Right," said Twilight, but she made no progress. At last, Twilight fell down, her eyes brimming with tears. "I'm sorry for wasting your time."
"No, Twilight. You can do it. Try one more time." As Twilight fought and tried, Celestia suddenly pounded her hooves, mimicking the Sonic Rainboom. But it did nothing but startle Twilight. The prism wavered in her grasp, then fell to the ground and shattered.
"With all due respect, Your Highness, this is a waste of time," Prime Factor said. "I'm sorry, Miss Sparkle, but your magic is not quite up to snuff for this academy."
Twilight looked up to Celestia. "B-b-but I studied so hard... please don't tell me I have to go," she pleaded.
Celestia sighed. "I'm sorry, Twilight. I... have a feeling you would have been a most faithful student," she said. She draped a wing over Rarity. "Come, my dear. We have much to discuss."
* * *
The Threads were unhappy, but Celestia did not understand why. They coiled and writhed as they wrote over one another and split apart. In her meditative chamber, Celestia felt awash in negative energy, of That Which Was Not Meant to Be. "What's wrong?" she cried out. "Why are you displeased?"
They centered her upon the Threads of Twilight Sparkle and Rarity. The two were locked in constant quarrel, but Rarity's was winning. It was Twilight's that hissed the most. It was... not unraveling, but shifting, mutating into some bizarre corruption of its old form. Suddenly, she understood. Twilight was the Cornerstone of something, what she did not know; some story greater than herself. She could not be shifted from the Great Plan without sundering it all. "Please, accept Rarity!" Celestia asked. "She can do what Twilight would, can't she?"
The Threads were upset at this. They told her the future, too fast for her to comprehend, information beyond pony understanding. She called out to them, "Stop! I must go back. Show me how this all took place. What has caused this disruption?"
The Threads slowly, slowly returned to rest. Then, they opened Celestia's eyes to the Time Beyond Time, the Space Between Space. And there, she followed causality back to a letter, a question, and a wish upon a star.
