"I simply cannot believe we have to do this," said Curio as the six ponies headed up to the staging area just outside the castle entrance where the male counterparts of the Equestrian rulers stood. "These outfits took forever to put on. I would never be able to live this down if I didn't look completely fabulous."
"Glad to see your modesty ain't changed a bit," quipped Applejune, receiving an icy stare from Curio in return. "Um, I mean no disrespect, Curio. You're certainly right about the outfits: we do look mighty sharp in 'em."
Curio smiled gently. "Thank you, Applejune."
"It's not like you're the pony who sewed them," Rainbow Rush murmured under his breath, just a little too loudly.
Curio scoffed. "What cheek! Of course I sewed them. I mean, technically my double may have done the work, but my inspiration produced the dresses they're wearing now, so it's essentially the same. Besides, these outfits are just divinely handsome," he giggled. "I daresay I've outdone myself this time. Or... we've outdone ourselves? Whatever."
Rainbow Rush sighed. "Ugh. Look, I'm sorry for being a jerk, but I'm going to be pissed until I can fly properly," he explained. "My center of mass is totally off right now, and I don't feel very awesome when I can't even make my body work right." Curio reached out to give Rainbow a hug.
"Alright guys, try to play it cool," Nightfall Twinkle whispered as he headed the procession up the stairs to where the other princes awaited them.
"Rainbow, what's done is done," said Flittercoy. "We know Nightfall Twinkle didn't mean to do any of this to us, and we've been in rougher spots before."
"Mmm-hmm!" concurred Bubble Pop, nodding vigorously. He had reluctantly Bubble Promised to a nervous group of friends to keep his mouth shut during the ceremony, not to mention several other things.
The six stallions reached the top of the stage, where two princes and a very concerned-looking little dragon stood. Five of them trotted off to the side to speak with Frill. Nightfall Twinkle tapped Celestia's counterpart with a hoof and whispered to him. "Um, Prince? Before we begin the ceremonies, I think you need to know... we may have a small problem," he said.
"How small, exactly?" came an unfamiliar voice from a familiar-looking pony. Princess Celestia's double had a shorter mane, but he was every bit as regal: he was even larger than she was, and his presence every bit as commanding. Luna's male counterpart walked over to listen in.
"I'm... not actually Nightfall Twinkle. This might be hard to swallow, but I'm a different Nightfall from a similar universe. It seems the six of us switched bodies with the six of them," he explained. "I was trying an experiment in the library..."
The male Celestia snorted. "Damn it, Prince. I specifically warned Nightfall Twinkle about doing experiments with other universes! And that means whoever I am over there must have warned you as well," he said. "I'm very disappointed in both of you."
"I'm sorry, Prince. You were right," Nightfall Twinkle said, lowering his head. "I honestly had no idea this sort of thing was even possible. I mean, I read through all of the literature, but I couldn't find a single case of mind transference across a dimensional boundary..."
Luna's double cleared his throat to speak. "The reason for that, of course, is Star Swoop the Braided," he said. "She kept ponies away from doing that sort of research in the first place, since it was so inherently dangerous. An instruction my brother and I, being pony, have also made the mistake of ignoring. Once each, I believe, although of... varying durations."
"Thank you, Mani," said a mildly annoyed white alicorn. "Alright, let's work with it. Prince Nightfall Twinkle, just exactly how different is your universe?"
Nightfall smiled sheepishly. "It's actually kind of bizarre: this universe is nearly identical to ours. The only notable difference is that, well... here, all the mares are stallions, and vice versa. Both gender and sex, to be precise," Nightfall said.
"Really? How fascinating. Female alicorns, what a novel idea!" he smiled. "Oh, where are my manners? I'm Prince Helios, and this is Prince Mani," said Celestia's counterpart, with a slight smile. "Out of curiosity, you are...?"
"Princess Twilight Sparkle. The others are Pinkie Pie, Rarity, Applejack, Fluttershy, and Rainbow Dash. Oh, and Frill is Spike, but that's your Frill there. They're probably explaining it to her now."
"Who are we? We—excuse me, I—am very interested!" said Prince Mani, his eyes bright.
"Princess Celestia and Princess Luna," said Nightfall Twinkle, waving his hoof with a bit of a flourish.
"I think we can ask these questions later, dear brother," Prince Helios chastised his sibling.
Prince Mani scoffed. "Oh, you sourpuss. At least tell us which sister is prettier," he said, winking at Nightfall, who immediately blushed.
"Wait just a moment. This universe, of all possible universes...? Twilight Sparkle, did you intentionally bring your friends here for your experiment?" said Helios, his eyes narrowing with a spark of anger flickering behind them. Prince Mani looked puzzled.
"What? Oh!" Nightfall Twinkle gasped, as the realization dawned. "No! I swear to you, Prince! Pinkie Pie picked a random set of coordinates to open a portal to, and this is, it's just what happened," the smaller alicorn said, dropping his head in shame. "I had no idea any of this was going to happen. I would never intentionally put my friends through something like this, no matter how much I might..."
"Excuse me, but what is this issue of which you both speak?" asked Prince Mani. "I am, if you would forgive the pun, completely in the dark."
Prince Helios bristled. "My former student and I need to have a private conversation about this, right now. I will discuss it with you in detail when we receive Nightfall Twinkle's friendship report on the same matter," said Helios. Prince Mani huffed and walked over to the other herd.
"Thank you for not telling him," Nightfall whispered, his muzzle downcast.
Helios nodded his head slowly. "Well, I think I shall have no choice but to tell him later, but you can be assured that he will keep it in confidence, just as I have. Now tell me about your universe. What other differences are there? It can't be completely identical, sex and gender aside," he said.
Nightfall shrugged. "Apparently, it can. As far as I can tell, this universe is perfectly symmetrical with our own," he said. "It's nothing at all like Equestria High, nor the alternate Equestria. Everything looks exactly the same, even down to the finest detail. In the library I noticed a stack of books beside me, and the orientations of each book were precisely the same as they'd been before we crossed over. Even the weathering and staining on one of the books was precisely the same."
"Perfect symmetry? That's very curious. You know, Star Swoop tried several times to access a universe in perfect symmetry with our own, but she never succeeded, because…" The Prince paused for a moment, deep in thought.
"I know, it's bizarre," said Nightfall, breaking the silence. "It's impossible that a global change to everypony's gender and sex wouldn't spiral out into even larger changes, so there must be some kind of force steering both universes together, correcting small imperfections as they arise. That might explain our names..."
"Your names?" Helios asked.
"Soon after we arrived, the names of our doubles became easier for us to remember than our own names. Our memories must have been tangled up in the transfer somehow, probably by that same force," Nightfall said. "In fact, we may still be connected. I think I can remember a few hazy details about Nightfall's past now, and I'm certain those memories weren't available ten minutes ago."
A worried look crossed Prince Helios's muzzle. "Twilight, I need to know exactly how this happened, but we have a ribbon-cutting ceremony to perform now. It should only take a few moments. I'll announce that the castle will be off-limits until the evening, which will give us time to fix things before you have visitors," he said.
"Ponyville has a carnival set up for the event anyway," said Nightfall. "The crowd will have plenty to do."
Prince Helios nodded. "Yes, I saw on my way in: your town has a remarkable way with celebrations, or so Prince Mani has informed me on more than one occasion. We'll do whatever is necessary to cover for you. In the worst case, Mani and I can play host to the castle while you and your friends work on a solution," he offered. "Now straighten yourself up, put on the best smile you can muster, and get ready to endure ten minutes of pomp."
"Whee," said Prince Nightfall Twinkle.