Sunset woke groggy and, even given what she'd already done in the past few weeks, a bit embarrassed. Though she thought it was likely she'd have a lot more sex with all of these girls, in the soberness of the morning after, she was keenly aware the night before had been a bit much. Caught in the moment, she'd risked impregnating Twilight - and had enjoyed the risk. The thought still brought her a twinge of arousal, but it was tempered heavily by the knowledge that she'd let her dick get the best of her, and that she'd really rather not impregnate anyone for a few years at least.

Of course, that also hadn't stopped her from doubling down on pumping the seed they now knew was fertile into Sonata, the one most likely to be receptive to it. She groaned, and wondered why she was up so early. She seemed to recall her dreams, wrapped as she was in breasts and legs and some still-damp fluids, had been far more pleasant than this guilt.

Then Twilight's phone beeped again. The purple girl groaned and sat up, unintentionally leaking a healthy load of someone's cum on to Sunset's leg. She fumbled with the phone.

"What's up?" Sunset whispered, though Rarity and Sonata were already sitting up. Sonata immediately leaned up against Sunset's shoulder.

"Applejack and Rainbow Dash replied to my warning text," Twilight said. "Let's see...Applejack's says 'call me,' that's probably not good. And Rainbow's says 'yeah, AJ and I hit that so hard, those pussies were tight'. I guess that explains it, but that doesn't seem good."

Before Sunset could say anything, Twilight's phone beeped again. "Email from Principal Celestia? Oh, it's to all seniors. For the first time since the Battle of the Bands, Aria and Adagio are putting on a concert? Noon today?"

"But it's Saturday," Rarity said.

"It says attendance is strictly voluntary," Twilight said, "but everyone loved their songs and they think they're harmless now, so I'm sure a lot of people will show up. Even if they can't enslave the whole school, I'm sure they can get enough magic out of it to cause a lot of trouble."

Sunset glanced at her own phone. "It's almost 11. Let's hurry."

"What are you going to do?" Sonata asked, voice trembling slightly.

"I dunno," Sunset said, "but we usually figure it out. You can stay here if you want, I'm sure. We understand if you don't want to confront your old crew."

For a minute she thought Sonata was going to take her up on it, but then she shook her head. "You helped me. It's only fair."

"Okay, but soon we really have to talk about," Sunset gestured to Sonata's belly, "this."

Sonata giggled. "Don't worry, I'm a siren. I've been pregnant loads before."

"Yeah, but you weren't a human teenager before! That's a big deal!"

"Girls," Rarity cut in, "I'm sure this is an important conversation, but I imagine Sonata won't be giving birth before noon. So if we're going to stop the other sirens, we all need to get in the shower, chop chop. No one will let us into a school function covered in semen."

Despite their hurry, it was nearly noon when they arrived at the school, and the lot was full of cars and bikes. They rushed to the auditorium, but as they approached the familiar sounds of the Dazzlings' music already echoed in the halls. They met the others just outside the auditorium.

"There you are!" Rainbow said. "We tried to get the principals not to let them on the stage, but they said we were being paranoid! What do we do?"

"Did you bring the instruments?"

"They're in the band room."

"I guess we improv, then."

They rushed to the band room and grabbed their instruments, then hurried back. Without amps, Sunset wasn't sure how they'd make themselves heard; she hoped their magic would take care of that. They burst in, instruments at the ready--

Only to find that nothing appeared to be amiss. Though Adagio and Aria were belting out on the stage, and sounded nice, there was no haze of magic in the room, and no one appeared to be quarreling or behaving strangely.

"Oh, are the Rainbooms up next? Groovy!" Tree Hugger gave a thumbs-up from next to the door, accompanied by scattered waves and smiles from other nearby students. On the stage, the Dazzlings glared at them. They finished the song, then jumped down from the stage and stalked towards their rivals. Shrugging, Flash Sentry took the stage with his guitar.

"You! You did this somehow," Aria pointed at Sunset, "or you, traitor!" She jabbed a finger at Sonata.

"Did what?" Pinkie asked.

"I don't know, but it isn't working! We took filthy loads from those two," she waved a hand at Applejack and Rainbow Dash, "and didn't even get our magic back!"

"Yeah, no" Rainbow smirked, "nice try, but you can't fake liking it that much. You didn't mind taking our loads."

Aria blushed, but Adagio just blustered on. "Well? What'd you do?"

Sunset shrugged. "I've got nothing. We just figured out your plan and came to stop you." The others shrugged too, except Sonata, who suddenly started giggling.

"What's so funny?" Aria demanded.

"You don't have any magic because your eggs are eating it all up!"

"What are you talking about, idiot?" Aria glared at her. "They took the safe potions!"

"Oh," Sunset said, realizing.

"Oh what?" Rainbow looked worried.

"We discovered it last night," Twilight said, "some of the bottles aren't labeled right, somehow. You must have taken the turbo-fertile ones by mistake!"

"Turbo...fertile?" Applejack asked slowly.

"Nonsense," Adagio said, "we aren't sexually compatible with filthy apes."

"But we are with ponies, and the potions always make pony sperm!" Sonata grinned.

"Oh whew," Rainbow said. "We're okay, AJ!"

"Yeah," Applejack said slowly, though Sunset thought her expression was mixed. Then, "wait, except we knocked up these varmints!" She pointed at the two sirens.

"Oh yeah," Dash sighed.

"This is the worst, Adagio," Aria yelled. "Your dumb plan didn't just fail, it got me knocked up by a monkey!"

"And you loved it," Dash reminded her helpfully.

"I just don't understand how we all used the wrong potion," Sunset murmured.

Suddenly from the crowed of stunned onlookers, laughter echoed briefly over Flash's riffs.

"Once again, the Great and Powerful Trixie has saved the school! No thanks to you, Lamebooms."

"Explain," Adagio glared at her.

"Well, after Sunset here spurned Trixie's generous advances, I broke into her locker. Clearly her disrespect needed to be punished. I didn't know what her bottles did, but I swapped all the labels. I thought they'd change it so her partner got the dick instead, but this is even better! Now I've gotten revenge and saved the school too! Trixie, away!" She dropped an unconvincing smoke bomb and fled, but this did nothing to prevent Adagio and Aria from tearing off after her.

"Why is no one else concerned that we have three unplanned pregnancies at our high school," Sunset sighed.

"I never planned on being a daddy," Applejack muttered.

"Silly, it's no big deal," Sonata said. "We've all been pregnant loads of times. Heh, loads."

"Sure, but you were...sirening. You're in high school now! You can't hide a big belly for nine months! Though I guess you'll graduate before you come to term..."

Sonata giggled. "That's silly. I'll eat salty foods for a few weeks then go lay our eggs down in the river. No one will even notice and I'll be done before prom. Unless you want to knock me up again."

"Buh?" Sunset said.

"She's not fully human," Twilight said slowly. "If she were, you couldn't have gotten her pregnant at all. She's probably right that she'll follow whatever reproductive cycle she always would if she mated with a pony."

"Duh," Sonata said.

"So...you'll be fine, and we'll have, what?"

"A bunch of seapony babies living down in the river!"

"Do you like...take care of them or anything?"

"What? No way, there are zillions, that'd be way too much work! Nah, the eggs will float down to sea and they'll take care of themselves."

"Wait," Applejack said, "so we just spawned a new species?"

"Well, new to Earth," Twilight said.

"Awesome," Rainbow said.

"Genetic diversity might be a problem...." Twilight muttered.

"Hear that AJ? Next time I'm doing Aria," Rainbow said.

"There won't be a next time, they called us monkeys! Like, in a bad way!"

"Eh, they'll come around, Adagio loved my cock."

Sunset tuned them out, and looked at Sonata.

"So...everything's going to be fine?"

Sonata nodded.

"How? I lost control of dangerous magic from another world! We impregnated three of our classmates! How did it just...turn out okay?"

Sonata shrugged. "You got lucky." Then she grinned. "You will again. A lot, if you want."

Sunset rolled her eyes, and was about to reply, when she became aware of a growing chant among the crowd.

"Rain-booms, rain-booms!"

"Your public awaits," Principal Celestia said, striding in the door. "I didn't expect this to be so popular. Unfortunately, Luna and I have another engagement. Twilight, as class president, can we trust you to lock up the school after everyone is done?"

"Of course, m'am!" Twilight jingled her spare school keys responsibly, though how that even worked, Sunset wasn't sure. It occurred to her that she would quite like to rail Twilight in the principal's office, in some kind of presidential formal-wear. She filed it away.

"Thank you!" Celestia and Luna hurried out, in an action Sunset was convinced was a legal nightmare, though it barely registered on the background weirdness of her life.

"Well," she gestured to the stage, "shall we?"

After two songs, the Rainbooms felt they'd done enough, and prepared to clear the stage for the next act. From the audience, though, came cheers for Sonata. Sunset saw her climbing to the stage, blushing.

"I guess you did miss out on the first act," Sunset said.

"Uh, duet?" Sonata whispered, looking scared. "I never sing alone."

Sunset shrugged, "sounds like fun."

She let Sonata take the lead, and the siren ran with it. She began a low, sensuous song, looking directly at Sunset, and Sunset felt the notes in her groin. She struggled to keep her pony penis from erupting, and looked at Sonata, eyes wide. Sonata just shrugged, but a little grin twisted her full lips as she sang.

Sunset didn't know the song; maybe Sonata was ad-libbing entirely. And after, she couldn't remember a single word. She wondered if this was a little bit of the siren's leftover magic, and glanced at the crowed, but nothing seemed to be wrong. So she embraced it, and ad-libbed back. Though she could never remember the words, she knew they got lower, softer, more suggestive as the two moved towards the mic. Once there, Sonata began dancing close to her as they sang, brushing bodies on bodies, and Sunset couldn't resist. Heat filled her as her cock reappeared, though even so she kept up the song.

Sunset, a bit worried, glanced at the crowd. Apparently she needn't have. Many were still cheering, and the rest were getting even more into it, making out or grinding on the dance floor.

Sunset shrugged and grinned back at Sonata. They danced close, running hands over each other everywhere, not caring who saw in the crowd below, still crooning out the deep, sexy song. Then Sonata twirled around Sunset, ending up standing between her and the crowd. In a dramatic pose, she stood legs askew and pressed one hand to the stage, then threw both hands to the sky, 'accidentally' catching the front of her skirt where it faced Sunset. The contact flipped it up just enough for Sunset to see Sonata's naked slit, and the moisture on her thighs. Then Sonata jumped.

Sunset wasn't sure how she saw it coming, let alone how Sonata knew she would, but her reflexes were up to the task. She found Sonata's legs wrapped around her, and her own arms were somehow below her, supporting her silky legs and firm ass. Sonata managed it wonderfully - her skirt had flipped up in the jump, and now lay around Sunset's stomach, leaving Sonata's dripping pussy separated from Sunset's eager pony prick only by the thin, strained fabric of her panties.

Sonata's song reached its peak, and she began winding it down. Sunset followed suit. As the last notes faded, Sonata reached one arm behind Sunset. First she caressed her rear, making Sunset shiver, then began tugging on the panties.

"This is why I never wear them," she whispered, "you never know when they'll be a pain."

Sunset blushed. "You're doing that up here?"

"I'm going to do you up here," Sonata corrected. "Unless you think they'd mind..." she nodded at the crowd.

Sunset looked out, and had to admit it seemed they wouldn't. What seemed like half of the grinders had shed at least some clothes, bras and panties, undershirts and briefs, thin cloth pressed to thin cloth, hands running over it. Tree Hugger was already naked, generous breasts bouncing as she danced. Pinkie, of course, was too, and had three members of the soccer team well on their way.

On the mats below the bleachers, Rainbow Dash and Applejack were wrestling, if you could really call it that. Both of their pairs of panties lay to the side, and Sunset could see flashes of muff as they tumbled, struggling over a potion bottle. As Sunset watched transfixed, Applejack rose triumphantly and chugged it, then buried a monster cock in Rainbow Dash unceremoniously as the other girl's eyes rolled back.

In growing surprise and arousal, Sunset's eyes roamed more. Rarity had Twilight by the hand, leading her towards the bathroom, then she caught Sunset's eye. She grinned and shrugged, and instead pushed Twilight to the mat, straddling her. She merely pulled their panties aside in her haste to be penetrated, and gazed at Sunset with a wink and licked her lips when she was.

Even as Sunset's eyes swept back to Sonata, she saw the room was progressing rapidly towards orgy. Another member of the football team she didn't recognize was bottomless and pouring lube on Bulk Biceps's massive, throbbing member. Muffins was eating cum out of Pinkie's pussy while both girls were double penetrated - Pinkie in the ass and mouth, Muffins in the ass and pussy. As Sunset watched, Pinkie took Thunderlane's shrinking cock out of her mouth and somehow wriggled around to face Muffins without dislodging Big Mac from her ass; she apparently hadn't swallowed, as she began swapping Thunderlane's cum with whatever Muffins had managed to get out of her pussy as the two began making out. Even as she did, Pinkie rubbed her newly moved crotch on Thunderlane's member; it was already stiffening again, and Sunset could tell where that was heading.

Even Lyra and Bon Bon, all protestations forgotten, were shirtless in each other's arms, making out openly, which for them seemed a bigger deal than Pinkie's personal orgy.

Finally, her eyes met Sonata's again. The siren was still smiling, and licked her lips. Then she glanced down. Sunset shrugged and nodded, and Sonata deftly pulled down her poor strained panties. Those in the crowd still watching let out a cheer as they fell to the stage. Sunset's cock slid directly into Sonata without Sunset even needing to do anything, though she felt a deft shifting on Sonata's part. The siren moaned, and Sunset staggered to the piano bench, sitting heavily, which only drove Sonata harder on to her, making both of them cry out in pleasure.

Sonata kissed her, then broke the kiss and grinned devilishly. Then, Sonata reached down and unbuckled her skirt. She threw it aside, revealing her full blue ass - and Sunset's shaft buried in her - to the whole assembled senior class. Hooting and cheering, plus some loud moaning, followed. Sunset blushed...but inside Sonata, her cock grew even harder.

"I thought I might not be the only one who liked an audience," the siren grinned.

"I didn't know I did," Sunset moaned, fighting to keep herself from cumming right then and there.

Sonata just grinned back, and leaned down to whisper in Sunset's ear. "Mmm, well, come on then daddy. Let's feed our babies."

Sunset nearly came just at that, but latched on to the mystery to keep herself grounded. She wanted to give their audience a show. She lightly bounced Sonata on her dick as they whispered to each other.

"Wait, what do you mean, feed them?"

"Ooooh, we're going to talk about this now?" Sonata moaned. "But, mmm, it's why the others didn't have their powers. Our eggs need magic! In Equestria our bodies make it. Here? Nope."

"Oh, so we'll need to do this a lot?"

"Well, I could have someone else do it, if you're busy."

"How often will they need it?"

"Once a day might be okay."

"Might?"

"Yeah."

"Sounds like we'll need at least two to be safe."

Sonata couldn't help but moan. "That does sound safer. Will you be able to do me that often?"

"For the eggs, obviously," Sunset said. "But you know, it'd be easier if we could do it before and after school. And that'd be easier if you lived at my place."

Sonata gasped in pleasure. "Sunset, are you asking me to move in? Just so you can inseminate me?"

"I didn't say just," Sunset gasped.

"Then yes," Sonata said, and clenched her pussy around Sunset as orgasm overtook her.

Sunset let herself go, then, her flare sealing off Sonata's pregnant womb. "I hope they're hungry," Sunset muttered, and Sonata shivered. Then Sunset lifted her partner up and pressed her back on the piano bench, pressing all the way inside her, and making sure to stay in profile, so the audience could see her load swell Sonata's belly. And then the dam broke. Ropes of cum surged into Sonata and she screamed in pleasure. Out of the corner of her eye, Sunset saw several people in the front row follow suit, cumming in, on, or with their partners, or just own their own, masturbating at the show.

Then Sonata's belly began to bulge as Sunset's massive load filled her. A gasp rose up from the crowd, then moans and at least one cry of, "get over here and do that to me!" Sunset glanced over and saw the orgy in the auditorium entirely renewed, partners going at it again, or in some cases newly, with most of the soloists in the front now paired or trioed off, taking each other in hand or mouth or pussy or ass. Even Fluttershy, looking half-mad, had tackled Big Mac and was riding him mercilessly, his thick farmer dick looking like it might break her, though she seemed not to mind.

The sight made Sunset shiver as her orgasm deepened, and still she pumped into her partner. Finally it was too much, and she pulled out, a huge gush of cum following her onto the poor piano bench. Still she came, drenching Sonata with her fertile cum.

Finally Sunset's dick vanished, and they stood. Gushes of semen fell out of Sonata on to the stage. Sunset staggered with residual pleasure. Sonata took off her cum-drenched clothes, then, naked, took a bow. She pushed Sunset into one, and then tugged down her skirt. Sunset found herself not particularly interested in resisting as she was stripped.

A cry rose up from the fornicating masses: "Encore, encore!"

"How do you have any left?" Sunset called to them incredulously.

"Oh, we'll show you what we have left, darling," Rarity, looking slightly cum-bloated herself, ascended the stage, bottomless but somehow still regal. She turned to a blushing Twilight and knelt, lifting the other girl's skirt. She began licking Twilight's naked slit, then transitioned seamlessly to fellatio as the other girl's cock appeared. The crowd cheered.

"Yeah, I still need to get a piece of this," Rainbow Dash slapped Applejack's bare ass as they ascended the stage on the other side, then chugged a potion and pressed Applejack on to the stage, sinking inside her. More cheers.

"I dunno who wants a turn," Pinky strutted up, basically covered in unidentifiable fluids, "but I probably shouldn't drink any more cum. Anything else is fair game!" For a minute only cheers greeted her, then Blossomforth came up and lay in front of her. Pinkie took the hint and started going down enthusiastically, wiggling her generous rump to show off the other options. After a moment, Fluttershy timidly came up behind her and took a lick of her pussy, and the crowd quieted down so as not to scare her off.

Sunset was surprised to notice her cock had returned. She was so aroused by the sight, she hadn't noticed the heat it brought. But Sonata had, and stroked it with a wicked grin. "Encore?"

Sunset shrugged. "Why not." She began to press Sonata down, ready to plunge in again, but Sonata stopped her.

"Hold on." Her partner fell to her hands and knees, raising her rump to spread her pussy, still leaking Sunset's seed. Sonata looked back at her. "Pony-style, so we can both watch their show," and she gestured to the audience, where once again coupling was in full swing. She looked around her at her friends, all exposed, in the throes of passion, on the stage. Letting out their inner feelings, just like with music. And then she felt it. The magic washed over her, and the familiar ears and tail appeared as she fully ponied up. All around her, she saw the same happen to her friends, who gasped, but were not distracted from their coupling.

"Oh, neat," Sonata said. "Well, stud, come on. Cover me. You know I'm in season." She wiggled her rear, and Sunset decided she was right. She sunk in, and everything became a blur of magic and pleasure again.

Luckily everyone got over their embarrassment and pitched in for the cleanup. It was regarded widely in the school as another "odd time", of which, after all, they'd already had several. Neither Sunset nor Twilight nor anyone else could find any evidence that magic had really been involved this time, rather than music and hormones and relief at the lack of magical catastrophe and, of course, senior year itself, the heady, somewhat magical realization that if you wanted to be naked with these people, this was approaching your last chance.

And, despite the general feeling of "odd time", several relationships did emerge, or become public, as a result of the special Saturday concert. Not the least of which, it turned out, was Sunset's. Of course, she didn't stop having sex with her friends. But it turned out she rather liked having Sonata around, and the feeling was mutual. So even after the few months in which "feeding the babies" was necessary, neither girl found themselves feeling much like moving on. Besides, as Equestrian expatriates, and ex-villains, they had a bond that few others did. Maybe that was enough. But that, perhaps, is another story.

And, of course, Apple Bloom (the other Apple Bloom) kept improving her potions, as ponies with cutie marks in alchemy are apt to do. And so, only a few months after that Saturday, still well before prom, Sunset Shimmer got another delivery from Princess Twilight, another case of potions. This time, rather than the yellow-label variety, the box contained both blue and red, with an accompanying note.

"Dear Sunset Shimmer,

Awfully sorry about the mix-up with the last batch. I had no idea it'd make you pony sperm even if you were a human! But good news, I fixed it! The red potions in there have my new alchemical anatomical adaption system, it's my own invention! They still do the same thing to the mare, or uh, woman, or whatever, where they bring her right into season, but they make sure your sperm's compatible! So whoever you're thinking about when you drink it, you'll be fertile with 'em all right.

They're real popular here on Equestria, and we've already got some super cool hybrid babies on the way because of 'em. Who knew how many ponies wanted to have kids with griffons or dragons or donkeys? It shouldn't come up over there, though, since you're all humans.

Oh, and I know you had a problem before with the labels getting switched, but don't worry, I made the new one so the potion glows red if it's the A.A.A.S. one. It's an alchemical glow, so it'll even glow if you mix it with something, so no chance of another mistake.

Well, hope you enjoy!

Apple Bloom"

Sunset rolled her eyes. "What the fuck, Apple Bloom. Why would you even send these again. I can't imagine what kind of trouble these could cause, let alone once we go to college."

"We'll probably find out," Sonata said.

"If Sonata's not really a full human," Fluttershy said, "are you, Sunset? If you took a red one and slept with, um, Rarity, would you have a centaur?"

"Why would you even wonder that," Dash asked, "that's weird."

"Oh," Fluttershy blushed, "n-no reason."

"We could just throw them away," Sunset muttered.

"Seems like a waste. You can't even get them on Earth," Twilight said. "We'll just have to put them in a bank vault or something until we find someone who wants to use one. Besides, imagine what I might be able to learn from studying them!"

"We are not doing more fertility field tests until we're actually ready to have babies," Sunset said, "but all right. You're right, no reason to waste them. I'll take out a safety deposit box."

And, in its own weird way, Senior Year went on.

THE END

Author's Note

Wow, that was impressive on my part - a multi-month break before the last chapter. Wasn't intentional, I promise - I knew roughly how it would end, it just took a while to find time to sit down and write it! Hopefully it was worth the wait.

Because this is the last chapter of the main story, I'm marking it "complete". That said, I have a couple of epilogue chapters in mind. Do you still ponder the unanswered questions:
-What was so important Luna and Celestia had to flee, allowing their students to get in a highly unrealistic orgy?
-Did The Great and Powerful Trixie get her comeuppance (or her cum-up-ins)?
-Will Lindyne come up with yet more absurd ways to have humans put magical pony dicks inside other humans?

I will probably issue some epilogue chapters answering these questions, but cannot promise it will be soon. So if that's your thing, you might want to leave this on your tracker.