Any spelling mistakes noticed, please send me a PM so I can fix them.

…

Twilight adjusted her goggles and glanced around the basement of the library, which at this time looked less like an old book storage room, and more like the lab of some mad scientist.

All the tables were covered with tubes and bottles, vials, beakers and all assortment of chemistry equipment.

The mare grinned as she carefully adjusted a dial, allowing only a single drop of a red colored liquid drip into a vial of rainbow colored liquid, which bubbled and hissed as the two fluids mixed. After a few seconds, the fluid changed from bright rainbow to a deep, purple-red color.

She checked her book on potions and smiled. Soon she would have a potion that would give any pony permanent wings. She had been working on this single potion for nearly a year now.

“Soon, just a couple more ingredients and I'll have that potion that Princess Celestia asked me to make for her...” She tapped her hoof to her chin. “But she already has wings. Why would she want a potion that can grant wings?” She shrugged and got back to work.

Another five chemicals were mixed into another beaker with exact precision. It mixed into a pearly white liquid after nearly an hour of painstaking work, with precise application of heating, cooling, and magic spells.

She added three drops of this to the larger vial, watching it change to a healthy pink.

“Two more.” She read the instructions carefully. “Hmm, Twenty four hours before I can add the next ingredient.” She sighed and set the vial into an enchanted lockbox and turned off all the equipment.

“Time to have something to eat.” Twilight set her goggles on the hook on the wall and headed upstairs.

“Spike?” She called out.

“Yes Twilight?” The baby dragon appeared from the upper library level.

“Is there anything in the fridge that's ready to eat?”

Spike smirked and rushed into the kitchen. “I made you your favorite daisy and daffodil sandwich.” He pulled the plate from the fridge and set it on the table. “I even added some of that lemon grass you've been telling me about. I hope it tastes alright.”

Twilight smiled and sat down and took a bite. “Mmm, this is good. We'll have to keep lemon grass in stock from now on.”

Spike shrugged and added 'Lemon Grass' to a list that hung next to the fridge. Said list was labeled 'Twilight's favorite foods.' “There we go. Lemon grass added.”

“Thank you Spike.” She finished off the food and stood up. “I'm going to go read a book and get some sleep. Set the alarm for sixteen hours. The next ingredient takes eight hours to prepare.”

Spike nodded and left the kitchen.

The Unicorn entered the Library proper and looked over the bookshelves. She spotted a book called Potions for Fun and Profit. Smiling, she selected it and headed over to her favorite reading cushion.

…

Twilight was shaken awake by Spike.

“Twilight, you fell asleep while reading again. You have an hour before you have to start making the next part of your potion.”

Twilight nodded and stood up, stretching the kinks out of her body. “I should eat before I get to work.”

“And take a shower.” Spike scrunched his nose. “It's been what? Two days since your last one.”

Twilight blushed. “Alright, alright. Shower, then food, then back to work.”

…

Clean and fed, Twilight rushed downstairs and started up all the equipment. Arcs of electricity between nodes, the hiss of the heaters, the bubbling of vials and all sorts of other sounds and scents filled her ears and nose.

Twilight made sure her goggles were clean and put them on. After checking the equipment to make sure there were no problems, she got to work on her assigned task.

She made sure she had water at hoof, to make sure she didn't get dehydrated, and made sure it was nowhere near where any of the potion ingredients could get mixed into it.

The mare was taking every precaution. One error and a year's work would be lost in an instant.

Her friends knew that she was working on a very important project for Princess Celestia, though there were times when it would be weeks between her workloads.

These last few ingredients had to be mixed together in just a few short days, and her friends knew, so they were not stopping by in case they might interrupt her, which would be bad.

And so Twilight worked tirelessly at making this miraculous and VERY expensive to make potion. It was a good thing that Princess Celestia was paying for everything, and sending over what she needed when she would be needing it.

Finally the second to last ingredient was completed, a blue powder. She measured out the exact amount, down to the grain and added it into the vial.

The liquid changed from the healthy pink to, oddly, a vibrant, glowing green.

The final ingredient, a Pegasai's primary pinion feather. Neither Rainbow Dash nor Fluttershy had any they had molted, so she had acquired one from one of the other ponies from the weather team. It was a good thing that Skyline had molted one of his just recently. Twilight had even given him a small pouch of bits in thanks.

Skyline was just happy to help, but the bits were appreciated as well.

Twilight used the feather tip to carefully stir the potion, changing it to a pure, luminous white.

“Finally, it's done.” She giggled with glee and put the stopper on the vial. She stored it in a small wooden box with thick, soft lining inside. She headed upstairs with the precious cargo and set it on the table. “Spike, send a letter to Princess Celestia. The potion is finished.”

“The letter is already written.” Spike grinned, holding up the letter. He then sent it off as requested. “And it's on its way. Oh yea, I made you a fresh salad for lunch.”

“That sounds wonderful. Let me know when you receive a reply. I need to personally deliver this potion to Princess Celestia as soon as possible.” She beamed and headed up into the kitchen. In the fridge, she found the salad and dug in.

No sooner had she finished, Spike walked in, carrying a scroll. “Here's the response. The letter is sealed, for your eyes only.”

Twilight felt giddy. She hoped that the Princess would be pleased with her work. Opening the letter, she read it to herself.

“Dear Twilight Sparkle, my most faithful student.

I am pleased to hear you have finally completed the requested Potion of Wings. It was a difficult task, but I am sure you are pleased as well.

And so I hereby state, this potion, brewed by one Twilight Sparkle, can only be consumed and used by the one who brewed it.”

At this point, Twilight froze. She read that line over and over again. “Only the one who brewed this potion can use it? But... I brewed it. I'm the only one who can use it? If I drink it, I'll become a winged Unicorn... I'll become like...” She couldn't fathom it. Princess Celestia had requested Twilight to make this potion... just so she could become an Alicorn? Become like Princess Celestia, Princess Luna and Princess Cadence? “I... I don't know what to say.”

She then resumed reading.

“The potion only maintains its potency for twenty four hours after the final ingredient is added. You have this time to decide if you would like to drink it and gain wings, or to leave it and remain the beautiful Unicorn you always have been.

Yours truly, Princess Celestia of Equestria.

PS, please make this decision on your own, tell none your friends of this until after your decision has been made.”

Twilight fell onto her rump, sitting and staring at the letter.

“Twi? What's wrong?” Spike asked.

“I...” Twilight looked at the letter when it suddenly flickered and burned away to ash. “I can't talk about it. It's something I need to decide on my own.” She got up and retrieved the box, then headed up into her room.

Setting it on her bed stand, she opened it and looked at the luminescent liquid. To become an Alicorn... She would have all eternity to learn magic and make friends and... But being immortal, she would have to watch her friends grow old and die. She was not sure she wanted that.

But she would have Princess Celestia, right? Again she looked at the vial. It was so tempting.

Immortality, the chance to live forever and learn all the magic that there was in the world. Again, so very tempting.

But the thought of watching her friends die over time. She didn't know if she could handle that. How did Princess Celestia manage? She was immortal, and she would outlive Twilight if she chose not to drink it.

What was she to do?

“I... I'd be able to spend time with all my friends. I can help them, and their families. That way, I can watch over them and their descendants just like Princess Celestia watches over all of us, all of Equestria. I... I'll do it.”

She picked up the vial and popped the stopper. There was little small, just a hint of mint, which was odd, seeing that there was no mint at all in the potion. She smiled and brought it to her lips, and tilted it back.

The taste, it was not minty at all. Rather, it tasted like everything she had put into it. In other words, horrible.

Twilight forced herself to swallow every last drop, not wanting to waste any of it, just in case.

She felt the potion hit her stomach and it felt like it was boiling, without producing much heat at all.

Then it started spreading through her body.

After a few minutes, the pain hit her with such intensity, Twilight Sparkle blacked out completely.

...

Twilight groaned as consciousness returned to a foggy mind.

Eyes opened, and instantly there was an odd weight on shoulders. Looking, a pair of magnificent lavender, feathered wings stretched out within view.

“I did it, I've be... come...” Hoof came to throat. “Why is my voice so deep?” Rising to stand, Twilight looked into the mirror... and nearly had a heart attack.

A stallion looked back at Twilight.

Wings went ridged as the slender, chiseled features were looked over. A handsome face, strong chest and legs, strong and nicely shaped hindquarters... and much to Twilight's horror...

A stallion's sheath, which most certainly held a stallion's penis.

Twilight spun around and lifted his tail... and failed to see a vagina.

She had, 100%, become male.

“Oh no... what am I going to do? Why did I become a stallion... A damn fine looking one, but STILL!” He frowned and thought about everything he had done when mixing the potion. Nothing had been done incorrectly. Everything had been done perfectly as the book detailed.

“Where did I go wrong? I have to contact Princess Celestia...” He levitated a quill and scroll over and wrote out what had happened after drinking the potion. Sure, Twilight Sparkle was now a winged Unicorn, perhaps a few inches taller than before, but she was now a HE.

A second letter for Spike with instructions to send the letter immediately, but NOT to read it under pain of no gems for the rest of his life. He slipped it out the bedroom door, making sure Spike was nowhere to be seen.

Now all he had to do was wait.

After an hour, Twilight heard Spike pitter-pattering outside the door. The sound of some grumbling, then the sound of him sending off the letter.

“If you're still in there Twi, I just sent out your letter, and no, I didn't read it. I want to keep my gem privileges thank you very much.” He then walked off to take care of some books that were still lying about.

Twilight sighed and turned back to the bed to lie down and think for a bit when a bright light filled the room, and Princess Celestia appeared.

“P-Princess Celestia?” Twilight dove behind the desk and cowered.

“Twilight?” Celestia sounded honestly surprised. “Please come out. I wish to see you. I had not expected this to happen to you.”

Twilight rose and stepped into view. He hung his head in shame. “I... I think I somehow made a mistake somewhere with the potion.”

Celestia picked up the vial and looked at the traces of luminescent white fluid. She cast a spell and analyzed the contents carefully. “Oh dear... Twilight, you did use a Pegasai pinion feather, correct?”

Twilight nodded.

“Was it from a mare or a stallion?”

“Um... Skyline is a stallion... wait...” His eyes went wide. “Do you mean too tell me that because of that one, final step, where I used a stallion feather, I became a stallion Alicorn?”

Celestia blushed a little. “I believe that may be the reason. I had not expected this to happen. It had not happened when my sister and I created these potions so long ago to become as we are now. We used our mother's molted pinions, and she, obviously, was a mare... I had not even thought that the gender of the feather would have any effect.” Celestia hung her head. “Can you ever forgive me Twilight? This is my entire fault. You are the first Unicorn since my sister and I with the magic power strong enough to become legendary Alicorns. We had the magic, and the knowledge how to make the potion.”

Twilight looked up and tried to smile, and only managed a weak one. “Well... I did it. I'm an Alicorn. I... I had never thought you meant for me to be the one to drink the potion. I thought, maybe, you had a Pegasus who had lost their wings in some horrible accident and this was meant for them, you know, to give them their wings back.” He looked at the mirror, his reflection. “I never imagined... It would be me.” He then smiled, a little stronger, more relaxed. “You know what? Mare or stallion, I am still Twilight Sparkle. I am still your protégé, and I still have so much I can learn from you.”

“Of course you can Twilight. But I can see I made a mistake now, and I will do all I can to rectify this, and restore your marehood to you.” Celestia nuzzled Twilight. She blushed as she breathed in the stallions scent. He was certainly healthy. “For now, I will teach you a spell that will allow you to appear as a Unicorn, though it cannot hide your gender.”

“Thank you Princess.” Twilight returned the nuzzle, and caught a scent she had never really paid any attention to before. Celestia smelled so sweet, and he could feel his body reacting. His wings stiffened, and he could feel something else happening between his legs.

Celestia noticed the growing scent and the warning signs and blushed, stepping back. “Oh dear. It would seem you are healthier than I expected.” She could easily see his larger than average shaft as it quickly reached full length. “I should teach you the spell right now.”

Twilight stepped back as well and tried to hide his member, his face quite red at the moment. He tried to fold his wings, but they simply refused to fold. “Yes... that might be a good idea... But... What about... this?”

Celestia giggled. “You will have to learn to master that all on your own. I believe you can do it Twilight.” She then proceeded, despite the obvious distractions, to teach Twilight the transformation spell.

Twilight learned it with ease, and after a single casting, his wings vanished, though he remained very male. It took quite a lot of focus, and a touch of magic, but Twilight managed to bring himself back under a semblance of control.

“Very good Twilight. Now, I must return back to Canterlot, with the book and what remains in this vial to try to find a way to reverse it.”

“Of course Princess.” Twilight opened the bedroom door and peeked out. Spike was nowhere to be seen, so the pair made their way into the basement to recover the thick book.

Once it was in Celestia's possession, she turned to the young stallion. “All I can ask is that you be patient.”

“Of course Princess.” Twilight bowed and watched as his mentor, teacher, and beloved Princess flared with light and teleported back to Canterlot. Sighing, he headed back upstairs and stepped into the Library Proper.

Right in sight of Spike.

“Hey Twi... light? Wait, you're not her. Who are you?” He growled, glaring at the oddly familiarly colored stallion.

“Spike, it's me, Twilight. I drank that potion that Princess Celestia asked me to make. Only the one who made the potion could use it, and the Princess felt that I was the first Unicorn in many thousands of years that had the magical strength to use it and become an Alicorn... As you can see, it didn't work as planned.”

“So... it turned you into a stallion?” Spike's eyes went wide. “But... how?”

“The feather I got from Skyline. He's a stallion. I was supposed to use the feather of a mare for the potion to work properly...” Twilight hung his head. “Princess Celestia is going to try to find a way to change me back into a mare. Until then, I'm stuck like this.”

Spike chuckled, and then started laughing, finally falling over and laughing as he rolled on the floor.

“Oh sure Spike. Yuk it up.” Twilight scowled, but she couldn't really blame him. He would have had a good laugh if Spike had become a girl dragon, and he knew it. Sighing, the stallion looked at the clock. “It's only midafternoon... and the library has been closed for three days in a row. I have to open it back up for Ponyville...”

“What will you tell the ponies who come in to borrow or return books?”

“Damn...” Twilight frowned. “I didn't think about that... I know, I'm Twilight's twin brother... do you think that will fly?”

Spike shook his head. “You already have an older brother. You know, Shining Armor? Married to Princess Cadence?”

“Oh... right...” Twilight frowned. “But how can I face my friends then? How can I face Ponyville like this?”

“Easy, you tell the truth.”

“Oh sure, tell them all I was making a potion that would turn me into an Alicorn Princess, but instead I get turned into a stallion...” Twilight paced back and forth. “But Applejack would be able to tell if I lied anyway. She's good at that. Pinkie Pie would know, and the same with Rarity. They're both so perceptive. Fluttershy, I can never lie to her. That would hurt her just too much, and Dash... Oh she is going to find this just to funny and I'll never live it down.”

Spike patted Twilight's shoulder. “Hey, I'll be here for you, always your Number One Assistant.”

“Of course Spike, I can always rely on you. Well, time to open the library up.” His magic opened the curtains and flipped the sign to open. He then unlocked the front door. “I'll just be up in my room if you need any help with anything. The library is yours for the time being...” Twilight selected a few books, seemingly at random, and floated them upstairs.

“Alright Twi. I'll call if I need help with anything.”

Twilight smiled at Spike and disappeared upstairs.

Spike sighed. “When the others get wind of this, it's going to be so funny to watch.” He then got to work, tending the library.

…

To be Continued...