Svengallop snarled as he stomped into his trailer and kicked the door shut behind him. The nerve of that mare! He made her a star and this was how she repaid him? Well, if Rara wanted her independence, she could have it. It would take him less than an hour to get everypony organized and out of this backwater. He'd even pull his own trailer if it sped up the process. And they certainly wouldn't need the Countess's palanquin, which would free up Pop and Lock to—

A knock on the trailer door interrupted his planning, followed by a voice on the other side saying, "Mister Svengallop?"

Svengallop nearly tore the door off its hinges as he opened it, then scowled at the mares bothering him. One was a white unicorn. The other... "Oh. Hello, Princess. Come for another recording session? How kind of you to actually warn me this time." Svengallop forced his lips into a smirk. "Why don't I go get Purple Rain? We can do this professionally."

The unicorn put her muzzle into the air. "Well! There's no need to be rude."

"After that stunt cost me my star client, I'd say there's every reason to be rude. You probably feel real proud of yourselves right now, don't you? Stopping the big, bad talent agent and saving the poor, innocent starlet." Svengallop threw his hooves into the air. "News flash, ponies! That star is falling thanks to you."

"I am Sapphire Shores's favorite costume designer," said the unicorn, giving him a flat look. "Between the two of us, I think we can get Coloratura another manager."

Svengallop snorted. "What, have Limelight look after her? You think he doesn't go for perks? He has Sapphire Shores convinced that changing managers will curse her for the rest of her life."

"At least he doesn't hold entire performances for ransom."

"Rarity!" The princess frowned at her companion. "I asked you to join me because of your experience in this industry, not so you could heckle Svengallop."

That got Svengallop to raise an eyebrow. He certainly wasn't expecting Princess Twily-Come-Lately to come to his defense. "Why are you two here, anyway?"

Twilight gave him a serious look that could give most record executives a run for their money. "I wanted to make you an offer."

"Did you now? And why should I listen to it?"

Twilight tilted her head behind her, towards the stage. "Can you afford not to?"

Svengallop rolled his eyes. "Please. You think Coloratura was the only client in my stable? Just watch. I'll have a C-lister on the top of the charts in a month."

"Will you now?" said Rarity, raising an eyebrow.

"What's that supposed to mean?"

"Your best client, the premiere singer in all of Equestria, walking out on you?" Rarity shook her head. "That's not going to look at all good. And trying to boost up somepony with less talent immediately after, well, that's only going to make you look desperate. And if it doesn't pan out? Oh, your reputation will be horribly stained. And, believe me, I know stains."

"Plus," said Twilight. "what if I told you I could get you three A-listers tomorrow? Ones who would really benefit from your particular managerial style?"

Svengallop scoffed. "I'd say you were crazy. Who? From where? And why even help me after convincing Coloratura to drop me like a hot potato?"

"The way you abused her trust and fame was deplorable," said Rarity.

Twilight nudged her with an elbow. "However, that still doesn't give us the right to destroy your livelihood."

Svengallop didn't know how she'd managed to rattle that off with a straight face, but he wasn't impressed. "Seems to give you the right to judge me all you want."

"I'm a princess, sir." Twilight spread her wings for emphasis. "Kind of comes with the title."

"Feh. I'm from Manehattan, Your Highness. I don't care about what you are, only what you can do for me."

"And I'm offering to save your career."

Svengallop chewed it over for a moment. "Okay, I'm listening. But Miss 'I Know Sapphire Shores' here needs to go."

"Gladly." Rarity turned with far too much flair and sauntered off.

Twilight had the decency to look sheepish. "I'm sorry about Rarity. She's had bad experiences with the dark side of Manehattan in the past."

That got a grudging nod out of Svengallop. "Haven't we all. Now, about this group. Any experience?"

"Centuries of it."

Svengallop's mouth worked silently for a moment."Don't tell me Princess Celestia's putting together a duet act with her sister."

Twilight blinked at that. "That's... quite the mental image. And no. However, they are going to need those vocal modulation spells."

"What happened to those centuries of experience?"

"Severe magical backlash." Twilight grinned. "They won't be able to sing a note without you."

Svengallop rubbed his chin. "Hmm. I like what I'm hearing. I'm guessing you don't have any recordings on hoof."

Twilight shook her head. "The logistics involved are... tricky."

Typical. "Can you at least describe their style?"

After a moment, Twilight said, "In a word, seductive."

"Oh, I can definitely work with that." The choreography started coming together in Svengallop's mind before he even realized he was seriously considering the proposal. "Of course, I'll want to meet with them personally."

Twilight nodded. "Of course."

The message was written, the mirror portal activated, and within a few hours, the sirens returned to Equestria... more or less.

"I have wings!" Sonata Dusk marveled at her new appendages. She turned to find that she wasn't the only one doing so. "You have wings!"

Sunset Shimmer nodded, mouth agape, entranced by her feathers.

Meanwhile, Adagio Dazzle scowled at Twilight, tossing her head and sending her hair bunching against her horn. "You can't possibly be serious."

Aria Blaze nudged her hard enough to send her stumbling. "Zip it, Adagio. This is the opportunity of a lifetime. And if you hadn't noticed, we only have one lifetime left."

"We are sirens. This is beneath us."

Aria glared at Adagio, thrashing her tail. "We were sirens. Dark depths, I can't fly or cast spells anymore."

Adagio harrumphed, her muzzle in the air. "We still have our pride. At least, I do."

"And right now, that's all you have." Aria pointed at Sunset. "We were on the verge of eating cat food before Princess Baconhair over there gave us the offer. We're out of money and out of options in the human world. Now look at us. We're back in Equestria, we each have a pony's worth of magic, and we'll even get to sing again. What more could you possibly want?"

Adagio gave her a dumbfounded look. "World domination. Obviously."

"Obviously," Aria said, rolling her eyes. "But if you had to choose between being surrounded by adoring masses who weren't mind controlled and starving in an alley, which would you pick?"

"Well..." Adagio tilted her head from side to side as she thought.

Aria wrapped a foreleg around Adagio's neck and drew her close. "Beach me if I know how, but Sonata actually has more brains than a brine shrimp now that she's a pegasus."

Both looked at Sonata, who was smiling sheepishly at Sunset. "'I'm sorry I thought your hair was edible on the way here. Seems kinda obvious in hindsight, you know?"

"Buh... I... wings..."

Aria nudged Adagio's gaze back at her. "You are not taking this away from me, Dazzle, do you hear me?"

"What I hear is insubordinatiackh!" Adagio floundered as Aria tightened her grip. The unicorn nodded frantically, and the earth mare released her.

Twilight watched Adagio try to catch her breath and collapse in the process. "Well?"

"Sonata and I accept," said Aria. "If Adagio can swallow her pride, great. If not, throw her back."

Adagio got back to her hooves and cleared her throat. "Before I accept, I must meet this agent of yours. We'll need to come to an... understanding."

Twilight nodded. "Of course."

The next day, Adagio and Svengallop sized each other up in the castle foyer. Their movements nearly reflected one another, their eyes narrowed in near-identical appraising looks.

Finally, Adagio broke the silence. "We're only doing this because you can help us sing again."

Svengallop smirked. "I'm only doing this because you can make me rich."

Adagio returned the expression and stuck out a hoof. "So long as we have an understanding."

"I'd say we do," Svengallop said as he bumped it.

"Fast forward a year later, and here we are!" said Sonata.

Coloratura looked around the Bitz-Carlton ballroom. "That's... very nice."

Sonata beamed. "I know, right? Best wedding reception I've ever been to. Also the only one."

After a few moments, Coloratura spoke up again. "I, uh, I feel like you may have skipped a few steps."

"Oh! Well, Adagio was really grateful once we could sing again. Like, really grateful." After a beat, Sonata added, "She wanted to fu—"

"I think I get it," said Coloratura, a little green.

"But Svenny wanted to make sure it was an exclusive thing first." Sonata nodded over to the table where the fiances sat, gazing at one another with lidded eyes like they couldn't decide whether they wanted to kiss or tear out each other's throats.

"I didn't expect Svengallop to be so traditional when it came to that sort of thing." Coloratura did expect him to want to keep something all to himself, but she wasn't going to say that to the bride's sister. At least, she thought the pegasus was Adagio's sister. She certainly wasn't going to ask her here and now.

"Totes romantic, right? And he would not budge on it. So they decided to go whole hog!"

Coloratura took a few moments to try to puzzle that out. "Whole... what?"

"Oh!" Sonata giggled. "Never mind. Expression from another world."

Probably best to not ask, thought Coloratura, who had spent enough time around Pinkie Pie to recognize the signs of a... different mind. "Well, that does explain how we got here, but you never actually answered my question."

"I didn't? Sorry, guess I lost track of things and stuff. What was your question?"

Coloratura pointed at two eerily identical orange mares by the buffet. "Why are there two Applejacks?" Indeed, they were far from the only ponies multiply present. Each of Applejack's friends had a doppleganger, including a wingless, bespectacled Twilight Sparkle who'd spent most of the party all but clinging to the side of an orange alicorn. Most ponies were keeping clear of both of them, not knowing what to do with them.

"Oh, right, that," said Sonata. "Adagio invited them. Said she wanted the girls who beat us to witness her ultimate triumph or something like that. And, well, they're both Applejack, so why not have both come, right?"

"Uh... right."

Author's Notes:

In the spirit of Valentine's Day, have some belligerent romance between two musical parasites.

Why are the Dazzlings ponies? Well, after the giant energy horse shattered their pendants, Twilight explicitly said they were "just harmless teenage girls." That, to me, implies they were rendered not just powerless, but fully human. By extension, that means that they should turn into ponies when going back through the mirror.
Hey, it makes at least as much sense as Spike turning into a dog.

(Oh, and if you're wondering, Pop Hit and Lock Step are two of the backup dancers from "The Mane Attraction." Just don't ask me which ones.)