Spike cast a nervous glance over to the corner of the library where Twilight Sparkle sat, hunched over a roll of parchment. Books, scrolls, and odd magical artefacts were scattered all around her, her mane was frazzled, and every so often, a manic giggle or squeal would erupt that made him wince.
A knock on the door drew his attention away from the disturbing sight. Opening the door, he found Pinkie Pie on the other side. "Oh, hey Pinkie Pie," he said.
"Hiya Spike!" Pinkie chirped. "What's up?"
Twilight emitted a particularly loud, foalish squeal. Pinkie and Spike both glanced over in her direction.
"What's going on with Twilight?" Pinkie asked in a quieter tone.
Spike shrugged. "She's working on something. She won't tell me what it is. This has been going on for three days now. She barely eats or sleeps."
Pinkie tilted her head, twitching an ear. "Well, whatever she's doing, it hasn't set off my Pinkie Sense, but...do you think we should be worried?"
Spike gave her a flat stare. "When is Twilight acting like this ever not a reason to worry?"
"Good point," Pinkie said.
Without warning, the entire room turned purple.
"Whuh-oh," Pinkie said, ducking. "TWILIGHT EMERGENCY! TWILIGHT EMERGENCY!" With that, she shot back through the open library door and ran screaming into the streets of Ponyville.
The weird purple glow faded. Twilight calmly turned and faced Spike with a broad, beaming grin. "Spike? Let's round up the girls. I've got a new spell to test."
* * * * *
Five puzzled, somewhat nervous mares stood in a line before Twilight and Spike. "I suppose you're wondering why I've gathered you all here," Twilight said.
"Oh! Oh! Are we suspects in a murder case?" Pinkie asked. "Because I have an alibi! And Rarity probably did it anyway."
"I would NEVER!" Rarity said indignantly. "Wait. Nopony's been murdered. Or have they?"
Twilight rolled her eyes. "No, Rarity, there hasn't been any murder. No, I've called you all here becaaaaaaaause..." She paused for dramatic effect, then flared her wings. "I've written a new spell, and I need a volunteer to test it on!"
Twilight's friends looked around at one another.
"Not it!" Rainbow Dash called.
"Not it!" Pinkie Pie echoed.
"Not it!" Applejack added.
"Um...not it...if that's okay," Fluttershy said softly.
"Absolutely not it," Rarity said.
"Rarity's it," Rainbow Dash, Applejack, and Pinkie Pie chorused.
"I just said no!" Rarity huffed.
"Yeah but you were slow, and we all called not it first," Rainbow Dash pointed out.
"But...I...!" Rarity stammered, stamping a hoof.
"You get wings again," Twilight said in a sing-song tone.
Rarity's ears perked up. "Wings? Glorious, beautiful wings?" She tilted her head. "Weeeelllll....I suppose volunteering wouldn't hurt. Heh. Anything for a friend, right?"
Twilight rolled her eyes and smirked. "Right."
Pinkie Pie tilted her head. "Wait a second. You said you'd written a new spell. But you've already done the give-a-pony-wings spell before."
"This is a new spell," Twilight said. "Just trust me. You'll love it. Ready, Rarity?"
Everypony except Rarity stepped back, giving Twilight and her guinea pig a wide berth. Rarity stood primly, steeling herself, as Twilight's horn began to glow. A bright violet-white light engulfed Rarity, lifting her into the air. Dazzling motes of light danced around her, nearly blinding her friends.
After two long, suspenseful minutes, the light engulfing Rarity exploded outward. When everypony could see again, they gasped.
Rarity hovered three feet off the ground. She'd gained well over a foot in height. Her mane and tail were streaked through with glittering gold and spangled with sparkling motes of diamond dust, and rippled in a nonexistent wind. Amethyst horseshoes graced her hooves, with a matching tiara and peytral upon her head and chest. Broad, feathery wings kept her in the air with steady beats.
The others stared at her, jaws agape.
Twilight grinned. "Yesyesyes! It worked!"
"You...you turned Rarity into an ALICORN?!" Rainbow Dash cried, eyes wide.
"I'm a what?!" Rarity gasped. She quickly conjured up a full-length mirror and examined herself. "Oh...oh goodness...this is...simply breathtaking...!"
"How did you do that?" Fluttershy asked softly.
"It's my new Princess-For-A-Day spell," Twilight said proudly. "It's really hard to cast, so I can probably only cast it once a week, if that, but it'll turn anypony into an alicorn for twenty-four hours."
"That's...that's AWESOME!" Rainbow Dash cried.
"Ooh! Ooh! Me next! Me next!" Pinkie shouted excitedly, bouncing up and down.
Twilight giggled. "Like I said, it'll be a while before I can cast it again. And it'll probably be a lot harder to cast on an earth pony."
"This will last a full day, you say?" Rarity asked as she touched down on the ground.
"One full day, and then you'll turn back to normal." Twilight paused. "Did it hurt?"
"It felt...tingly," Rarity said. "But no, it didn't hurt."
"Good. I was worried it might."
"Hey Twi? Question," Applejack said suddenly. When Twilight turned to her, she continued, "How is it that you turned into a for-real, permanent-like princess, an' so far, apart from growin' wings, you only got a little taller, but this spell o' yours gave Rarity here th' whole pie?"
"That's a good question, Applejack," Twilight said, smiling. "I actually asked Princess Celestia about my physical changes, and she said that Cadance took a while to grow into her...princessy-ness...too. That's why when I was writing the spell, I factored that in. The spell turns ponies into the equivalent of a fully matured alicorn."
"Well, I'm certainly loving the results, darling," Rarity said with a toss of her mane. "Is there anything special I need to know about this spell? Any cautions?"
Twilight shook her head. "Just be careful to remember when it's going to wear off." She glanced up at the Ponyville clock tower, just visible in the distance. "It's a quarter past one right now, so...if I were you, I wouldn't go flying after lunch tomorrow."
Rarity chuckled. "Right, I'll keep that in mind." She tilted her head. "So...what should I do with this newfound princessly glory?"
Twilight shrugged. "Anything you want, I guess. Of course, I'll be sticking close to you to keep an eye on you, take measurements, monitor the spell...just make sure nothing happens I wasn't expecting."
"But of course," Rarity said, nodding. "Well then...I suppose if I'm going to be a princess for a day, then I deserve some proper pampering." She lifted off from the ground, tossing her shimmering mane. "Off to the spa!"
"The spa? Seriously?" Applejack asked flatly. "How's that any different from how pampered you normally are?"
"It just is," Rarity said snootily before flying gracefully away. Twilight rolled her eyes at her friends, then followed her.
Once the two alicorns were gone, Applejack turned to the others. "Bets on how ugly this whole thing's gonna turn?"
"Aww, don't be like that, AJ!" Pinkie Pie said. "This could actually be really fun!"
* * * * *
Rarity magicked open the doors of Ponyville's premiere (and only) spa and strode boldly through. "Princess Rarity has arrived!" she declared.
Aloe and Lotus trotted into the receiving area, took one look at Rarity, and swooned.
"Yes, I know...I do have that effect on ponies," Rarity said airily.
Twilight facehoofed. "Rarity...don't you think you're overdoing it just a—"
Rarity whirled on her. "Let me live the dream, Twilight. Let me live the dream."
Twilight sighed, rolling her eyes. "Fine, go ahead," she said with a faint smile.
As the spa ponies recovered, they stared openly at Rarity. "Miss Rarity...you are now a princess as well?"
"For a while," Rarity said. "My dear friend Princess Twilight Sparkle has invented a spell that will turn a humble, everyday pony such as myself into a fabulous alicorn."
"For a day," Twilight added, resisting the urge to facehoof at Rarity's dramatic antics.
Aloe and Lotus looked at one another, blinking, then back at Twilight. "Truly?" Aloe asked. "Does it only work on unicorns?"
"Oh, it'll work on anypony," Twilight said cheerfully.
The twins looked at one another again. "US! USE IT ON US!" they said as one.
Twilight laughed sheepishly. "I...can't cast it again today," she said. "It takes a lot out of me. And I really need to monitor Rarity to make sure nothing goes wrong with the spell." She frowned, raising a hoof to her muzzle. "And...I'd really rather use a pegasus as my next test subject before I try it on an earth pony." She smiled. "But! If everything goes well, sure, you girls can have a turn if you want. You'll have to go one at a time though." She paused. "Aaaand it's really only fair if I let my closest friends go first, after everything they've been through with me. You understand, right?"
The twins nodded. "Of course, Princess," Aloe said.
"It's only fair," Lotus added.
"Well then!" Twilight said, smiling. "The usual, ladies!"
"And do pay extra care to my fabulous wings," Rarity said, tossing her mane.
* * * * *
Later, after a hooficure, a mineral bath, and a thorough preening for both alicorns, Rarity felt the need to strut around town, showing off her radiant beauty for all to see. Twilight followed along, nonplussed at Rarity's antics. "You'd think after what happened in Cloudsdale, she'd have learned her lesson," Twilight muttered to herself.
"Oh, but I did, darling," Rarity said, having overheard her. "I haven't flown any higher than I know I can fall without hurting myself, and I'm not going to. But I can still flaunt this generous and gracious gift you've given me!"
Twilight shook her head and chuckled. "Okay, fine. I guess a little strutting and prancing is okay."
"Well, I've always said that if I had the good fortune to become an alicorn like you, I'd flaunt it. And now I can!"
Ponies murmured excitedly as Rarity strutted past in all her glory. She flared her wings, tossing her head this way and that, smiling radiantly upon the citizens of Ponyville. This went on for almost an hour before Rarity and Twilight mutually agreed to drop by their favorite cafe and have a late afternoon snack.
By evening, all of Ponyville was abuzz about the newest princess in town, and rumors and gossip were flying left and right.
* * * * *
Twilight and Spike spent the night at Carousel Boutique. Sweetie Belle had nearly fainted when she saw her sister; she spent most of dinner squeaking out questions.
The following morning, when Sweetie Belle opened the front door to leave for school, she discovered a massive crowd outside Carousel Boutique. She quickly alerted Rarity and Twilight, who trotted outside to face the masses, with Twilight teleporting Sweetie past the crowd so she could continue on to school unimpeded.
Twilight cleared her throat loudly and raised a hoof to motion for silence. Once the crowd calmed, she addressed them:
"I understand that seeing another alicorn in Ponyville is exciting, and some of you may be wondering how Rarity became a princess. Well, the truth is, she's only going to be a princess until about one this afternoon. This is just a new spell I'm testing. Once it wears off, she'll be the same old Rarity again."
"But in the meantime," Rarity added, "please feel free to admire my fabulosity! And perhaps do some shopping? I'm having a special today, twenty percent off everything!"
Many ponies went about their business, satisfied or disappointed. Others lingered to ask Twilight questions. Still others remained to do some actual shopping, or simply to admire Rarity, who basked in the attention.
As the day wore on, Twilight continued to observe Rarity, Rarity continued to enjoy the temporary boost in popularity, and the two met up with their friends for a late lunch. By the time they'd assembled a sumptuous picnic feast and migrated to their favorite picnic spot, the spell had worn off, and Rarity was a unicorn once again.
"Thank you, Twilight," Rarity said. "Even if it was short-lived, being a princess was quite the experience."
"You certainly did seem to enjoy it," Twilight noted with a smile.
"Yes, well...let's just say that I realize now, with even greater certainty, just how little you truly appreciate your own good fortune."
Twilight rolled her eyes. "Now, Rarity. You know how I feel about being a princess. I'm still the same pony I've always been."
"Still," Rarity said, "perhaps in a few years, when you've finished maturing into a proper alicorn, you'll see it differently." She shrugged. "In any event, it was fun while it lasted."
"Yeah, and you sure caused a stir in town!" Rainbow Dash said. "A lot of ponies are excited about this."
"Yeah, Rarity prancin' around all fancy sure worked ever'pony up somethin' fierce," Applejack agreed.
Rarity's eyes suddenly shone brightly. "Twilight! I just had an excellent idea!"
"Oh?" Twilight asked, tilting her head.
Rarity placed her hooves on Twilight's shoulders. Her eyes were positively sparkling. "You...you could sell this."
"Sell it?" Twilight asked, frowning.
"Hey now. That actually ain't a bad idea," Applejack said. "Ah bet a lotta ponies would pay t' be a princess fer a day."
Twilight blinked. "I...no. I couldn't possibly charge money to cast a spell on ponies! Especially one that wears off after a day..."
Fluttershy, surprisingly, spoke up. "Why not? Trixie charges ponies to watch her do silly tricks. And most ponies don't even really enjoy her show that much." Everypony stared at her. She ducked her head. "Um...I'm sorry...was that too mean a thing to say?"
Twilight frowned. "Well, it's true that Trixie is more tell than show, but..." She shook her head. "I just don't think..."
"Well...everypony has the right to gain from their special talent," Rainbow Dash said. "So...I don't see why you couldn't rent out your little spell. I mean, you wouldn't have to charge ponies a lot for it. Just enough to make it worth your while, you know?"
"You did say casting it takes a lot out of you," Pinkie pointed out.
Twilight's muzzle wrinkled and her ears twitched as she thought it over. "Well...I'll think about it. I still need to perform a few more tests. You know, to make sure it'll work on all three types of ponies, and that it'll work consistently." She smiled around at her friends. "But I wouldn't think of charging any of you for it."
"Then we'll be happy to be your test subjects!" Pinkie declared enthusiastically.
"We will?" Fluttershy squeaked.
"Sure we will," Rainbow Dash agreed.
Twilight grinned. "I'm glad you all feel that way. Especially you, Rainbow Dash. Because for the next test, I need a pegasus."
Author's Note
And so begins the spiritual successor to Let's Be Evil. There won't be reader voting for this one, though.
This is one I'll mostly be working on in between my other projects, when I need to work past writer's block, or when I just want to write something short, silly, and fun that I can squirt out in a couple hours.
Next time, Rainbow Dash gets horny. 
