Serendipity was skimming through her notes one more time when Azahar answered her knock. "Oh hey there Serendipity. Didn't realize you were off-shift. What's up?"
"I was hoping to show you something. It's just you there, right?"
"Yeah, everyone else is either lucky enough to be gallivanting around Equestria or unlucky enough to be working overtime filling in for them. Come on in?" Azahar stepped back out of the doorway, and Serendipity trotted through and hopped onto the bunk facing hers. "So what have you got there?"
"Oh, just some notes on a spell that might let me deal with the Quench." Serendipity made a point of not looking up from her review, and had to fight to keep the amusement from her ears and face as she watched Azahar through the corner of her eye. "I figured you might have some interest in seeing me try it out."
Azahar bounced forward on her bunk. "Would I? I suppose that's one way to put it." She leaned toward Serendipity with a grin. "So, what's this going to look like? How does it work? How were you—"
Serendipity cut her off with a raised hoof. "Ah-ah-ah, shouldn't that be a surprise? We wouldn't want to spoil the fun." She smirked at Azahar's conflicted look – she might not be great at judging most human expressions, but a face that couldn't settle on one for more than a moment conveyed emotion all its own. After a quick scan through the remainder of her notes confirmed the spellforms she held in her mind matched those on the paper, she floated them across to Azahar's bunk and sat herself up in as close to a human posture as she could maintain. "Alright, time to see if this works."
As Serendipity began to draw off magic from the converter, Azahar grew mildly alarmed. "Hold on, does that mean you haven't tested this before?" Though Serendipity's talent let her keep far more pieces of information straight in her mind simultaneously than most ponies, it didn't mean she could divide her focus onto all of them at once, so by the time she registered what Azahar had said she had already poured more energy than she'd ever needed for anything but teleportation into her spell's foundational forms. "Shouldn't we have some kind of emergency backup here or something?" And there were so many more fiddly bits all trying to wriggle out of control that she couldn't spare an instant to do anything beyond note that the words on Azahar's tablet did, in fact, exist. A distant part in the back of her mind almost sideswiped her efforts into calamity by observing that it felt not unlike trying to perform the Clockwork Tower drill if all the gears were made of blackberry jam.
Azahar cut herself off when the magic leaking from Serendipity's spell grew intense enough that it began to glow in real light, and she shielded her eyes with her communications tablet as she averted her gaze. Serendipity felt a brief and faraway touch of thankfulness for the drop in distraction, but it was quickly replaced by a sustained and closer touch of panic as she had to draw more power than she'd ever used before just to keep her ever-more-intricate spellforms from bleeding away enough energy to fall to pieces. By the time she managed to lock them together into their stable holding configuration, her coat and mane were standing on end from more than just alarm. The moment her racing mind slowed enough she could think again, she poured in the burst of magic needed to complete her spell as she directed it to take Azahar as its template.
The book she'd found in Princess Twilight's Heavens Gate library hadn't given any real detail on what the transformation itself would entail, so Serendipity had spent many nights dreaming of how it might go. Would her coat vanish across her body like a shadow fleeing from the sun as a pegasus pushed a cloud aside, or would it disappear in a flash as if they had bucked the cloud apart instead? Would her hooves wrack her in agony like when she'd torn off a shoe as they branched into fingers and toes, or would they be as painless as if she had overdosed on morphine? About the only possibility Serendipity hadn't considered was that the transformation would be like a teleport – in a burst and a blink, everything around her shifted.
Serendipity got a split-second impression of Azahar staring at her in utter shock, and then she reeled where she sat as a vast wave of heat and fatigue crashed through her. A huge blast of brilliant sparks pulsed out from her and briefly filled Azahar's dormitory with noon-bright light, leaving her vision dazzled and dim. She heard Azahar yelling something and reached out a hand to reassure her, but as she instinctively stood to cross the aisle to her bunk, she staggered beneath a deluge of faintness.
Serendipity was lying on her back. That was odd.
And it was odd that it didn't feel odd. Ponies were supposed to lie on their bellies.
Ponies were. That made more sense. Serendipity cracked open an eye and held an arm in front of it. Yep, hand, though the colors looked weird. She let it fall to touch her face and giggled in surprise. It was bizarre – the sensations were alien in the most literal sense of the word, yet so natural she couldn't conceive of anything else.
Strange-sounding footsteps to the side caught her ear, and as she turned her head she realized it wasn't just her hand – all the colors looked weird. It was like some mad painter had taken all the colors of magic and mixed them into everything, so that even the bedspreads and Azahar's clothes gleamed with latent power. Was that how humans were supposed to see, or was it just because she was a unicorn underneath the spell?
Azahar spoke as she sat by Serendipity's legs, and Serendipity marveled at the tones – it was like her pony ears had been listening to a record so scratched even the faintest hints of meaning were nigh-impossible to glean, while her human ears heard a perfect copy for the first time. "Well, I've got to give it to you, you definitely got the surprise part down. I definitely didn't wake up today expecting to meet a twin I didn't have." Serendipity still couldn't follow Azahar's words by sound alone, but it was merely the impossible of a language she'd never learned to speak, not the impossible-impossible of sounds her brain simply wasn't optimized to process. "So, are you feeling alright?"
Serendipity nodded and cast out her mind to grab her marker and whiteboard, then started as she realized the blindingly obvious. It was possible she hadn't thought everything through.
Azahar smirked teasingly. "Finally noticed one of the flaws in your plan, eh? Well don't worry, we'll figure something out. You've even got a visitor who's an expert at it." She glanced across the room, and Serendipity followed her gaze as the subtly-off sound of hoofsteps drew near.
At first Serendipity had no clue who her visitor might be – it was as though the magic that seemed to pervade the room had been drawn wholly out from their coat and mane and tail, leaving just their base colors of deep dappled grey and near-black shot through with hints of dawn rather than the vivid masking hues that had always pressed against her horn when looking at a fellow Worlder. She'd known she wouldn't be able to see cutie marks as a human and was as ready as she could be, but somehow she hadn't made the obvious connection that it was because she wouldn't be able to see any magical colorations. But far more disconcerting was that even their basic details seemed... fuzzy to her mind, and she couldn't tell anything about them, even whether they were a mare or a stallion. And then a writing-board of some sort and a human tablet sprung free from their bags as they sat down before her, and far more immensely, intensely disconcerting was that she couldn't sense the slightest hint of magic from their floating objects or their horn.
Her visitor's expression shifted subtly, but for some reason Serendipity couldn't put her hoof on what it meant. "My apologies; I didn't mean to discomfort you. I know this is a lot to get used to." The instant she spoke, her scriptboard blazed with glowing English text and her tablet filled with Equestrian. Serendipity vaguely noticed something seemed wrong about the way her words sounded, but was too consumed by stunned realization to pay any heed – she had to be Princess Twilight.
"No, don't get up! You don't need to bow. Especially after I let you down so badly." Serendipity dropped back into the same human sitting position as Azahar, and giddy wonder that she'd moved with such ease overshadowed her confusion at the Princess's words. "Now, I suggest we start by seeing how good your handwriting is. If that skill carried over, it will make this a lot easier."
Serendipity imagined she looked as utterly baffled as Azahar did. Princess Twilight promptly elaborated. "Many ponies think of transformations as simply reshaping the body while leaving the mind unaffected. However, as you may be aware, all transformations between living creatures must alter the mind to some degree to allow it to regulate the new form's vital functions and to integrate its sensory channels. Although Lath recently reopened the debate on whether or not the basal layers responsible for those processes should really be considered part of the mind proper as such, and he makes some valid points that—" The Princess shook her head. "I'm sorry; lecturing is a hard habit to break. Perhaps I should simply summarize. Most transformation spells don't just incorporate autonomous functions and innate instinct, but also include a significant amount of the template's or templates' learned skills. You may have noticed that unlike a young foal or kid, you can perform basic movements without difficulty. It's possible that you also copied Azahar's procedural memory for more complicated actions such as writing."
It took most of Serendipity's concentration just to keep up with Princess Twilight's galeforce delivery, with old words vanishing from her tablet and scriptboard to make way for the new in a dazzling tempest. However, with so much lecture in a single squall, Serendipity couldn't help but hornpoint what had struck her as amiss with the Princess's speech – it sounded as if she were talking through an immensely thick fog while carrying a mouthful of blankets, until all the modifiers had been muffled away and only vague impressions of the base tones remained. But even if that strange realization were enough to break her focus, the last, most-important sentence hung still and bright after the Princess fell quiet.
"Whoa, really? That's kind of creepy but really cool." Azahar bounced in place and looked expectantly at Serendipity. Serendipity nodded and focused back on Princess Twilight, who floated over a whiteboard and marker from her bags.
Serendipity instinctively grabbed them in one smooth motion, then paused. After a moment, Princess Twilight spoke up. "Don't overthink it; it should come as naturally as taking hold of the marker did. Though it might help if Azahar showed you how?"
"Sure." Azahar reached over and took the Princess's marker, and scribbled "Ta-da!" while she spoke. "So considering why this all started, I have to ask, why didn't you just give everypony those glowy boards from the get-go?" She showed off the way she was holding it, then pressed it back into Serendipity's hand.
"We did consider it, but making the enchantments compatible with earth ponies and pegasi was complicated enough that the supply would have been severely limited for some time. Especially since— here, hold this for a minute, would you?"
Azahar paused in her adjustment of Serendipity's grip, then shrugged and grabbed the offered scriptboard. It immediately pulsed with a blast of glowing sparks that tingled warmly on Serendipity's skin as they washed over her, and its writing blinked out.
Princess Twilight took it back as Azahar shook out her hand. "Since humans and enchantments don't get along any better than ponies and human microelectronics." The dark scriptboard flashed and began to glow with English again as she spoke. "It was much more practical to simply recruit from the existing pool of scribes. And furthermore, doing so was a perfect way to increase contact between ponies and humans, and give them the chance to form new friendships." The Princess bobbed her horn from Serendipity to Azahar and back.
Azahar smirked triumphantly at Serendipity, then glanced at her execrable attempts at handwriting. "Hey, not too shabby. I think. Maybe Twilight can understand it?"
Princess Twilight spun her whiteboard around and squinted at it. "How did I let you down so badly?" Her ears dipped, but to Serendipity's frustration she couldn't tell if it was with embarrassment, sorrow, or something else entirely. "This situation is ultimately my fault. I might not have been directly culpable, but I'm the one whose directions let you slip through the cracks, so I'm the one responsible."
"What do you mean?"
"Before today, the very possibility of magical transformation was classified on this side of the Gate, except as wild tales like in the various cartoon adaptations, pending a way to assuage Earth's governments' fears and avert any possible panic. When we first discovered how the Quench breaks conventional transformation spells, I decided the best way to respect that while keeping everypony safe was a hidden embargo on the subject, same as we use in academia for normal permanent transformations. But I obviously failed to adapt it properly for the new setting, or else Serendipity would have been identified as a candidate caster and warned."
Azahar whistled. "Applejack cannot have been happy about that."
"She wasn't, but she ultimately agreed after she couldn't come up with anything better." Princess Twilight snorted. "And then she tried to use it as another reason why we shouldn't make her a Princess."
Serendipity finally managed to get her handwriting halfway legible. "Aren't permanent transformations supposed to be so hard that nopony can ever figure out how to cast them?"
Princess Twilight shook her head, and her bearing shifted halfway back to lecture-mode before she caught herself. "They're actually far simpler than temporary transformations, and only difficult to cast because we intentionally teach the principles of magic in such a way that the student has to unlearn years of instincts to make them work. If permanent transformations were cast often enough to imprint on the aether..." The Princess shuddered. "Well, surges would be absolutely terrifying. Customs discouraging raising foals around high-magic institutes exist for very good reason. We don't want ponies to end up like you did, or worse."
Azahar glanced over at Serendipity and gave voice to her fears. "So does that mean Serendipity is stuck as my twin forever, then?"
Princess Twilight shook her head again, and Serendipity slumped in relief. "It's not quite so dire as that; I could transform her back into a unicorn without difficulty. The problem is... well, to put it in human terms, the spell she used creates a program to restore the target's original form and stores it locally in an enchantment, with contingencies in place to run it if that enchantment would be altered by an outside force. Unfortunately, those contingencies were in no way designed to deal with the target being transformed into a lifeform whose magic is expressed as any type of Quench. Since we don't have any external backups of her original form, that information is lost. I could use photographs and recordings to approximate her appearance, but otherwise it's a complete reroll of the dice for physical traits, magical affinities, and so on."
That sent Serendipity rigid, and after fumbling with the Princess's marker for a moment she simply gave up and waved it at her hips. Princess Twilight cocked her head, and then her ears perked up. "Oh! Your cutie mark is a reflection of who you are, so you don't need to worry about losing it. It might change over time now that you don't have an external anchor to keep that part of your self-image from drifting, but whatever it becomes will perfectly represent the pony you are when you're transformed back."
Serendipity's racing heart slowed back towards a human's rapid resting rate, and she managed to recover her meager handwriting skills. "As long as that's true, I can live with the rest."
Princess Twilight smiled. "That's good to hear." She spun her tablet around and looked at it briefly. "I need to go deal with more of the fallout from this so I can get back on schedule. I'll meet with you again soon to cover everything else. I suggest you see how much progress you can make on your handwriting before then." A surprisingly-simple lunch-purse floated out of her bags and came to a hover in front of Serendipity. "I imagine you're probably getting hungry, so I took the liberty of bringing you some food. Hopefully it will keep your spirits up." Before Serendipity could figure out how to grab it without dropping anything, Azahar came to her rescue and plucked it from the air. "I hope you have a good evening."
Serendipity pointed her hand at Princess Twilight and nodded, and Azahar called out "You too" as she pulled the lunch-purse open. The Princess rose and turned for the door, with her scriptboard and tablet dancing through the air into her bags as she went.
As the Princess's tail disappeared past the doorframe, Azahar muttered something under her breath, and Serendipity turned back to see what she'd said:
"Oh come on Twilight, not you too. Don't encourage her."
Serendipity tilted her head, and Azahar rolled her eyes and held out a packet with a gloriously familiar design. "Apparently your thieving ways are now royally sponsored. Why is this my life?" Serendipity grinned, and Azahar sighed, opened the packet, and passed her a slice of pepino.
Her grin lasted right up until it hit her tongue.
Serendipity squeezed her eyes shut and swallowed. "It doesn't taste good like it did when I was a pony."
Azahar eyed a slice critically, then popped it in her mouth. She chewed for a moment, then her eyes went wide with mirth and she doubled over cackling. The moment she recovered, she fixed Serendipity with the smirk to end all smirks and grabbed another slice. "Now that's what I call karma."