Author's Note
The unicorn Rarity who went through the mirror is going to be called just Rarity.
The human Rarity who lives in the human world will be referred to as Diamond. (You'll see why later in the story)
Through the Portal
Rarity used her magic to sew the last button onto the jacket she was making for Mrs. Harshwhinny.
"Done!" the unicorn smiled, picking her beige creation up with her blue stream of magic.
"Thank you so much, Rarity." Harshwhinny was already in Carousel Boutique, waiting for her article of clothing to be done. She walked up to Rarity, five bits in her hoof, and exchanged them for her new coat.
"No problem at all," Rarity said, her proper voice filled with joy. She loved when customers were satisfied, even when those satisfied customers hardly smiled.
Harshwhinny walked out the door, as Rarity trotted to her bedroom, flopping down on her frilly bed. She started to close her eyes, exhausted from the long day of making outfits, as Twilight burst in. The unicorn was alerted by the bell that rung whenever somepony opened the door.
Rarity scowled to herself, and walked back into her office/making room.
"Hi, Rarity. This isn't a bad time, right?" Twilight asked, her voice sounding raced.
"No," Rarity lied. "This is a perfect time. Is there something you need, dear?"
"Yes. I need you come to my house."
"Why? Is something wrong?" Rarity's face struck with worry.
"Sorta," Twilight sheepishly replied, dragging the mare out of her home.
They went all the way to the alicorn's new castle, which was gleaming purple.
"I still love your new humble abode," Rarity remarked, her friend still urging her to come inside.
Spike was on his tummy, on the floor, spitting scrolls out of his mouth. His spikes lay flat on his head, his eyes completely dull.
"Princess Celestia's sending us letters of all sorts," Twilight explained.
"H-help me," Spike croaked, before shooting another letter out of his mouth
"And?" Rarity asked.
"I don't know why she's doing it," Twilight continued. "I'm going to read over all of them eventually, but they won't stop coming. It's just like the day Celestia sent a bunch of my friendship letters to remind me that we have a friendship that cannot be undone when Discord corrupted us all."
"I'm sorry to be rude, but what do I have to do with this?" Rarity wondered.
"Everypony else was busy," Twilight told her, dully.
"So.. What do we do?"
"Well, could you help me read all these scrolls?" Twilight picked one up with her magic.
"Sure." Rarity also grabbed one and plopped herself down on the couch, reading it.
"Hmm.." Twilight scanned her violet eyes over the paper. "Report to the Canterlot castle immediately?"
"That's what this one says as well," Rarity implied.
Twilight ran her eyes through each of them, picking them up, as more came from Spike. "All of them say the same thing!"
"Well my best guess is to go to the Canterlot Caste," Rarity suggested.
"Good plan. Let's go!" Twilight dropped the scrolls, and picked up her baby dragon, putting him on her back.
The two unicorns ran outside, Twilight spreading her feathery wings.
"I'll fly you there," she said.
"Do you think that's the best idea?" the white mare pondered. "No offense, but you aren't the world's greatest flyer."
"Oh come on!" Twilight rolled her eyes, as she picked Rarity up by her sides. She started to flap her wings, stirring up dirt and dust from the ground. She lifted herself into the air roughly, shaking the baby dragon and the unicorn in between her hooves.
"Please don't drop me. Please don't drop me," Rarity silently prayed.
Twilight started to fly forward, her aerial stance improving slightly. She steadily flapped her wings, keeping on the trail to the glimmering castle in the distance.
Spike dropped a few more scrolls, which Twilight figured were just the same thing.
"Hold in there, Spike," Twilight brought up the pace in her flying, the castle approaching faster.
"I-" He sent out another scroll. "I'll try."
The alicorn finally landed on the ground of Canterlot, managing to wipe a flower bed out, as she landed on her face.
Rarity picked her face up from the dirt, wiping some of the grub off. "Twilight, do you mind getting up?"
"Sorry, Rarity," Twilight said, brushing herself off a bit before standing.
Spike belched another letter, and another, and another, until the three of them finally made their way into castle.
The guards were expected them, and instantly let them in.
"Princess Celestia," Twilight bowed. Rarity did as well.
"Princess Twilight," The mare bowed back.
"Why were you sending us so many scrolls with the same thing on them? What's going on?" Twilight frantically asked.
Spike still lay on his belly, but the letter burping had stopped.
"I've sorry I hurt your tummy, Spike," Celestia apologized. "But it was urgent that you come. Er.." She was about to tell her why she had come, but she looked over at Rarity.
"Is there something wrong?" Twilight said.
"I don't mean to be rude, but why did you bring your one friend, and not all of them?"
"Everypony else was busy."
"Oh." Celestia cleared her throat. "Just as Discord had betrayed us, so has Sunset Shimmer."
Twilight, Spike, and Rarity gasped.
"I know, it's surprising. But she stole another important item; The Music Box."
"The Music Box?" Rarity asked, her nose slightly scrunched.
"Yes. It's a very important item in the human world," Celestia explained.
"What's it do?" Twilight asked.
"Just like the Tree of Harmony, it contains the power of friendship. However, if it is stolen, friendship will be turned against each other. And that's just what happen."
"Why would Sunset Shimmer even want it?" the purple unicorn wondered.
"She wants everypony to turn against each other," Celestia told them. "She does not realize that even she will turn against everypony eventually. But I do not think that minds her."
"So what must we do?" Twilight said.
"You need to go back into the mirror."
"Got it!" Twilight smiled.
Rarity stood there blankly, her mind racing. "The human world?"
"Oh yes, you didn't come with Twilight on her last quest there," Celestia reminded herself. "Would you like to go, Rarity?"
Her crystal eyes sparkled. "R-really? My goodness I'm honored," she gushed.
Celestia nodded, a grin on her face.
Rarity started to squeal happily to herself, silently.
The alicorn princess leaned into Twilight's ear. "While this may be a fun adventure for Rarity, I want you to stick to your mission, okay?"
"Got it," she replied.
"Come along," Celestia guided them to the room where the mirror portal was hidden.
Rarity felt her heart jump with excitement as Celestia started to explain things.
"You only have three days once again," she told them, mostly aiming toward Twilight. She could tell Rarity was far too excited to listen to rules. "Or else you'll be trapped in there for thirty moons."
Twilight nodded, along with Spike, who had finally recovered from his belly ache.
"Whenever you're ready," Celestia said.
Twilight walked up to the portal, stuck one hoof in, and then took it out. She bit her lip, still a bit nervous, and quickly walked into it.
Next came Spike, who bravely walked in.
Rarity took a moment to admire the glistening mirror. She smiled happily, and stepped into it.
