Princess Celestia and Sunset Shimmer reclined on large piles of plush velvet pillows in Celestia's spacious royal chambers. "You have no idea how much it delights me to see you again, Sunset Shimmer," Celestia said softly.
Sunset smiled, ducking her head. "I wasn't...I wasn't sure you'd ever want to see me again," she said.
"Oh, Sunset," Celestia said, shaking her head. "The last time we saw each other, I...I was exasperated and frustrated. I lost my temper."
"Yeah...I don't blame you," Sunset said miserably. "I was out of control."
"Yes, you were," Celestia said, "but that doesn't excuse my behavior. I made the same mistake with you I once made with my own sister." She sighed. "You would think, after a thousand years of remorse and regret, I would not repeat my greatest mistake." She perked up suddenly. "Which reminds me! You simply must meet Luna as soon as possible! I've told her so much about you!"
Sunset smiled. "I'm looking forward to it." She paused. "At least, I think I am. I've gotten used to Vice-Principal Luna, but meeting the princess who became Nightmare Moon..."
Celestia's muzzle twisted into a pained grimace. "I...would recommend not bringing that up," she said. "Luna's past is still a bit of a sore subject for her."
"I can relate," Sunset said with a shaky laugh. "I've pretty much gotten past the whole 'I turned into a literal demon' thing by now to the point where I can laugh about it with my friends, but it's not really something I like having thrown in my face."
Celestia blinked. "A demon? Twilight didn't tell me about that." She paused, then admitted, "Actually, Twilight didn't tell me much of anything about her time in your world except that she showed you the magic of friendship and that you were turning your life around and making friends."
"Really?" Sunset asked. "That doesn't sound like Twilight."
"It isn't," Celestia said. "I knew she was keeping something from me about what happened in your world because her report was...far less detailed than I'm used to. I figured there was a reason for it, and let it go. Besides, she's a Princess and my equal now, it isn't my place to question her."
"Nopony's your equal, Princess Celestia," Sunset said.
Celestia rolled her eyes. "Let an old mare have her little delusions." They both giggled. "So...do you want to talk about it?"
Sunset sighed. "There's not much to tell, really," she said. "I put on Twilight's crown, the Element of Harmony turned me into a demon, Twilight somehow made a magical connection with the human versions of her friends here, they blasted me with a rainbow, I woke up in a smoking crater in the middle of the school courtyard." She shrugged. "It took months to get everyone to stop glaring at me and muttering angrily behind my back—or to my face—and accept me as a changed person, but my friends stuck by me." She laughed softly. "Helping save the school from the Sirens went a long way toward changing everyone's opinion of me."
"The Sirens," Celestia said, shaking her head. "I can't believe Starswirl did something that irresponsible. I am truly sorry you and your friends had to deal with such a dangerous magical threat."
Sunset shrugged. "At least some good came out of it. Twilight figured out how to open the portal because I needed her help. Now we can go back and forth whenever we want."
"And that is truly a joyous thing," Celestia said with a smile. "I do hope you will be coming back to visit more often. Or...or perhaps even come home to stay?"
Sunset smiled a bit sadly. "I...don't think I'm coming back for good," she said. "At least...not yet. Not for a while. I've never been as happy as I am right now. I have friends, I have a good life."
Celestia's smile turned sad, but she nodded. "As long as you are happy and well, that is all I need. Though perhaps before you return home, I'll create another pair of enchanted journals...so you can keep in touch."
"I'd like that," Sunset said. She paused, then softly asked, "Princess Celestia?"
"Yes, my little pony?"
Sunset cast her gaze to the pillow she lay upon. "I...I was never going to be a princess, was I?"
Celestia sighed. "In all honesty? I'm not sure," she admitted. "I wanted it to be you. I hoped so dearly you were the one I'd been waiting for. That it would be you who would reunite the Elements of Harmony and save my sister when she escaped her imprisonment." She paused, then added, "I saw so much of myself in you that I conveniently forgot something very important."
"What was that?" Sunset asked, tilting her head.
"The third Cutie Mark on the trunk of the Tree of Harmony," Celestia said. "When Starswirl first took Luna and myself to the Tree, we did not yet have our Cutie Marks, yet they were already present on its trunk: the Sun and the Moon. It was not until we returned to the Tree to take the Elements of Harmony to defeat Discord that we truly realized the implications." She paused, studying her hooves. "There was a third Cutie Mark on the tree, larger and more prominent than ours. I believe Starswirl, who had already visited the future and seen many things to come, knew whose Cutie Mark it was—had seen Equestria as it is now, with four Alicorn Princesses." She bowed her head. "For many hundreds of years, I watched and waited. I desperately wanted to know who the third Cutie Mark on the Tree of Harmony belonged to.
"But then the time for my sister's return drew nearer, and I became desperate. I knew that a pony with powerful magic would need to recover and reunite the Elements of Harmony, and that only true friendship could revive their power. When I took you as my student, I...I hoped it would be you who would accomplish this." She looked away. "I hoped so strongly that I allowed myself to forget about..."
"The third Cutie Mark on the Tree," Sunset said quietly. "It's...it's Twilight's, isn't it?"
"It is," Celestia said, nodding. "I met her not long after your...departure...on the very day she earned her Cutie Mark. I immediately took her as my student, though I was more careful and more patient with her. And did not make the same mistake of promising her something dangerous."
Sunset laughed a short, bitter, self-deprecating laugh. "Wow," she said quietly. "I went through all that for nothing, huh?"
Celestia winced. "Well...the important thing is you ultimately found your purpose and your happiness. Even if it came at...at a terribly high cost."
They lapsed into an awkward silence.
"Well on the bright side," Sunset said suddenly, "as much as I miss having magic, I actually kinda like being human."
"Oh?" Celestia asked, her ears perking with interest.
"Yeah," Sunset said, smiling broadly. "When you get used to it, it's pretty cool. Magic may not be a regular thing there, but the human world is full of amazing things. Things I can't even explain in terms you'd understand!" She closed her eyes, a look of bliss crossing her face. "There's so many simple, little things that I enjoy. Riding my motorcycle, sitting barefoot in the park, feeling the cool green grass between my toes..." She smirked and looked at Celestia. "And my human form is pretty sexy. I'm looking forward to bikini season! Going to the beach with my friends, making all the guys drool..."
Celestia giggled, covering her muzzle with a hoof. "My goodness!" She smiled happily. "I know just enough about your world to understand that last part," she said with a wink, which sent both mares into giggles. After a long moment, Celestia sighed wistfully. "It's been a long time since we sat and laughed together."
"It has, hasn't it?" Sunset said. With a smile, she added, "We'll just have to make up for lost time..."
* * * * *
After a sinfully restful night in the luxurious suites of Canterlot Castle and a large, elegant royal breakfast—at which they were introduced to Princess Luna—Twilight led Sunset, Kim, and Ron deep into the catacombs beneath Canterlot.
"Wow. This place is...KP, what's the word I'm looking for?"
"Dank! That's the word. This place is dank."
"And dusty," Kim commented. "And—ew!" She ducked under a cobweb, idly trying to brush some strands of spidersilk from her mane with a hoof.
"We're almost to the Athenaeum," Twilight said.
"Just what the heck is an Athenaeum anyway?" Ron asked. "And if we're supposed to be doing research, wouldn't it be better to go to, y'know, a library?"
"An Athenaeum is a library," Sunset said as the group reached the base of the long, crumbled stone steps that emptied out into a massive cavern lit by ancient magical torches.
"Really?" Kim asked, looking around. "Because it kinda looks like a cross between a museum and someone's grandpa's basement."
The group descended into a massive cavern full of books, furniture, knick-knacks, museum pieces, artifacts, scrolls, tomes, globes, and the relics of a life devoted to magical research. Even overgrown with roots and fungus as it was, even with much of the carefully-wrought masonwork and furniture in a state of decay brought about by centuries, even with spiderwebs everywhere and bats rustling about in the stalactites high above, the grand space took the breath away from those who had never laid eyes upon it before.
Sunset looked around the ancient, dusty cavern, her eyes wide with wonder. "It's real," she breathed. Her muzzle crinkled. "Funny, I thought there'd be more books."
"Oh, this is just the antechamber," Twilight said. "The Athenaeum is further inside."
The group trotted through the antechamber, craning their necks around to gawk at everything, from an ancient, still ticking grandfather clock to a dusty old ship in a bottle. The sound of water trickling from overhead drew near, and they soon found themselves walking past a small artificial pond, inside which...
"HOLY HEE-HAW WHAT THE HECK IS THAT?!" Ron brayed.
Kim looked at what he was staring at, and recoiled in disgust. "Eugh!" In the pond lay a moldy, slimy, massive skeleton, its bones splayed out in the stagnant water. Four skulls lay half-submerged in the water, covered in algae.
Sunset leaned forward with interest. "Is that a hydra?"
"Was," Twilight said. "Come on, this way."
They trotted past the hydra corpse through a broader cavern; eventually, they came upon a huge carved stone building, built right into the rockface of the cave. Cracked sandstone sculptures of lions flanked the steps leading up to the tarnished bronze door. A brass plaque mounted on the door bore the legend:
ATHENAEUM AND SUNDRIES
"Looks like the Middleton Public Library," Ron said. "Only, y'know...a lot older."
Twilight's horn lit up, and the ancient bronze doors swung open.
Sunset glanced at her curiously. "You...you've been here before, haven't you?"
"Yeah," Twilight said. "Long story and I'll probably end up telling you most of it while we're doing research, but you're not the only pony who went through a magic mirror and caused everypony a lot of problems." She paused. "Err...no offense."
Sunset rolled her eyes. "None taken," she said. "Wait, what other pony? I don't remember you ever chasing anypony else through the mirror..."
"It wasn't the same portal," Twilight said. "It was another one of Starswirl's mirrors." She sighed. "Let's just say Celestia decided to visit her old boyfriend and we nearly lost Equestria in the process."
Sunset blinked. "Her...her what?!"
"Wow, Romeo and Juliet much?" Kim asked, shaking her head.
The group followed Twilight through the doors of the Athenaeum, which led to an anteroom full of dusty, cobwebbed old bookshelves stuffed full of tomes of forgotten lore. Jars and bottles lined shelves long overgrown with creeping vines that snaked through cracks in the rock and stone. Moss covered the ancient wooden shelves.
"Yeah this is a wizard's library," Ron said.
Sunset stared at a coatrack standing off to one side, from which hung an old purple cape and a hat adorned with bells. "Is...is that...?" she asked, her jaw dropping.
Twilight smiled. "The original," she said with a touch of pride. She gave Sunset a sly look. "Wanna try it on?"
Sunset's eyes bugged out and her ears folded back. "C-can I?" she whispered reverently.
"No," Twilight said with a smirk. At Sunset's crestfallen expression, she giggled. "Just kidding. Knock yourself out. I reinforced the preservation spell that's kept it from disintegrating all these years, so it's safe to move it."
With a look of pure awe, Sunset took the old hat and cape from the coatrack and gently put them on, ignoring the cobwebs and frayed threads grabbing at her coat. "Wow," she said, studying herself.
"Wizardy," Kim commented.
Sunset spent a moment posing and preening in the old wizard's garments, then gently put them back on the coatrack. "But...Twilight," she said, "if you found that here, if...if you preserved it magically..." She shook her head. "Why did you leave it down here? It belongs in a museum!"
Twilight smiled. "It is in a museum," she said. "A special museum. The secret museum. The true shrine to Starswirl the Bearded."
"Well, yeah, but—"
"It belongs down here," Twilight said firmly. "It's as much a part of him as this Athenaeum. As long as his hat and cape are here..." She looked around fondly. "He's still here." She smiled sadly. "Besides, Starswirl travels across time and space like the rest of us travel across town to grab a hayburger. I want it to be there waiting for him if, you know...if he ever pops in." She turned away from the coatrack. "Come on, what we're looking for is deeper in."
"Wait, there's more?" Ron asked.
"There's a lot more," Twilight said, heading for a descending staircase hidden in a shadowy alcove between two teetering old stacks. The quartet descended the stairs into a truly massive cave, half of which was overtaken by massive granite bookshelves, built three stories tall, with stone staircases and ladders set between the stacks, which were crammed full of books, scrolls, and tomes. The rest of the cavern was a reliquery, with various and sundry artifacts, knick-knacks, bric-a-brac, sculptures, lanterns, books, maps, charts, junk, and treasure scattered haphazardly in all directions. A massive sandstone carving of Starswirl himself towered over the cavern, near a two-story-tall painting of a much younger Celestia.
"Now this is a library," Kim said in an impressed tone as she looked around.
"It is," Sunset said giddily. "It really really is."
Twilight smiled and hovered off the ground, spreading her hooves broadly to encompass the totality of the grand space.
"Welcome," she said, "to the Athenaeum of Starswirl the Bearded."