I will probably post this whole fill to AO3 as well.

...

“Prompto, this day just gets weirder and weirder…”
“Yeah, I noticed. You actually called me instead of shooting a text.”
“That’s not what I mean. Gladio is a pot of flowers, Ignis is singing and dancing everywhere—“
“Wait, what? Gladio is what?”
“…A pot of flowers.”
Noctis pulled the phone away from his ear as Prompto burst into laughter.
“Oh man! You gotta send me a picture!”
“No way in hell. He’d murder me in my sleep.”
Not to mention, he’d likely be found quickly if he tried to hide out. Several servants had come up to his room, wishing him well and asking if he needed anything. One had even sent well wishes from his father. Which likely meant just about everyone knew he was hiding out in his room. He thanked the Six that this also meant his father was in a meeting with the council, which was likely where Clarus was as well. The head Amicitia likely wouldn’t be searching for his son or the prince any time soon. Not that it would matter if Gladio didn’t turn back before the meeting was over.
“Prompto,” Sniffle. “You gotta tell me. How long did it take for you to turn back into you?”
“Uh, sorry man. Can’t help ya there. I fell asleep a chocobo and woke up a Prompto, so it could’ve happened at any point during the night.”
“Damn.”
Noctis really did not need Gladio to remain a pot of flowers for an entire night. If it took that long. He also felt a little guilty about having Ignis sing and dance everywhere, for who knew how long, as well. A little. It was kind of entertaining.
“So, what are you gonna do?”
That was a good question. What really was there to do? He had no idea how to control the excess magic resulting from his sickness. He wasn’t even sure how his magic was making this happen, but then who was he to question the crystal’s magic. It was a gift from the gods after all. It likely held more power than any of the Lucian royal line could hope to understand. All it was used for was combat and protection, so there was no telling what else it had the power to do.
Considering the increasing number of penguins roaming the city and the citadel, Noctis wasn’t sure he wanted to know what else it could do.
“What’ll you do with Gladio?” Prompto asked after a period of silence. Noctis shook his head, though he knew his friend couldn’t see him.
“I don’t know. I can’t just leave him sitting around somewhere. But I have no idea when the…the…when the magic…Achoo!”
Noctis pulled his cellphone away from his face as he let loose yet another sneeze. He braced himself for the subsequent screams when yet another flock of penguins would appear from nowhere.
They never came.
Shrugging and figuring he just got lucky this time around, he put the phone back at his ear.
“Sorry, about that. Anyway, I was saying—“
“Uh…Noct? That you?”
Noctis raised an eyebrow at the question. Who else would it have been?
“What are you talking about, of course it’s m—“
He paused. Cleared his throat. Paused again.
Cleared his throat again.
Coughed.
And then he looked down.
“…”
“…Noct?”
“…”
“…You still there?”
… … …
“What the fff—“
From that day forth, Prompto would never let Noctis forget the screech that came out of his mouth. He would forever remember that moment with extreme amusement. Currently, however, he was lamenting the loss of hearing he would likely be experiencing. Not that it wasn’t still funny. Prompto thought he had it bad, being turned into a chocobo. His poor best friend was now a—
“How the…? What the…? Why?!”
What did Noctis do to deserve this? How in the hell did he even get sick? He rarely got sick! And never before had it caused such disastrous results. The last time he caught a cold, he laid in his bed like a good boy and ate the soup Ignis made him with slightly less complaint than usual. That was it. No turning his friends into weird shit. No singing and dancing. No flightless bird infestation. No…this!
“Okay, okay! Calm down, Noct! Take this slowly…”
“Prompto, you’re not helping!”
“No, no, I’m gonna help you through this. Just calm down, okay? Deep breaths…”
Deciding to humor his friend, Noct inhaled deeply through his mouth (he couldn’t really breathe through his nose anymore) several times. Surprisingly, he found himself calming down, albeit slowly. Prompto spoke soothingly the entire time.
“Alright. Now I want you to do something for me okay?”
“Okay?”
“Alright?”
“Alright, I’m listening.”
“You ready?”
“Yeah, get on with it.”
“Okay, listen carefully Noct. I want you to open your camera app, take a selfie, and hit sen—“
Prompto’s giggling could be heard for a split second before Noctis quickly hung up and tossed his phone over to his bed, scowling. It landed next to Gladio and Noctis shot the pot of flowers a glare as well.
“I better not hear shit from you about this,” he grumbled at the flora. While he was still unsure of whether or not Gladio was conscious in his current state, he could swear he could almost feel the smug aura coming off the plants. Clearing his throat, he got up again to head to his connected bathroom and finally blow his nose. The stuffiness was starting to drive him insane.
And, he had to face the music, he couldn’t really deny that he was curious. Grabbing a wad of tissue from the counter, the box left there from who knew how long ago since he never really used them, he stuck it up to his nose just as his eyes met his reflection. His clothes hadn’t changed. Still wearing his school uniform, jacket and all. His hair hadn’t changed. It had hung limply since morning, seeing as he was too tired and stuffy to style it, yet it retained the same length and same sick dullness. Yet, as he moved the tissue away from his face, he found himself staring at, well…not his face. He’d been told, to his annoyance, that he was ‘pretty’ before, but he’d never thought his looks particularly feminine. Yet now his jaw was softer, his face rounder, the contours smoother. His eyes shot down to his collar. There was no visible adam’s apple. He refused to allow his vision to go lower, not quite ready for another look at what was likely the cause of additional weight on his chest. His eyes instead flicked back to his face. He’d seen pictures of his mother before. If he hadn’t known better, he’d have thought he was looking at her through that mirror.
But he did know better, because if his mother was here now she would be just as regal as in the pictures with her long, beautiful hair and her pretty gowns, and she wouldn’t be the idiot in the school uniform, covered in snot and red-faced and tired and summoning penguins every time he sneezed.
She would probably be laughing at him, actually. According to stories from his dad, she laughed at him all the time when he ended up in some dumb situation. This would have probably made her day.
That at least brightened Noctis’ mood somewhat. The idea that he could have made his mother laugh. It kept his mind off of the likely opposite reaction he’d get from his father. He could see him shaking his head at Noct already, calling him his ‘wayward son’ and dragging him into more magic lessons so that this situation wouldn’t happen again. Noctis figured, as he finally actually blew his nose, that he might just need those extra lessons.
He had no idea his magic could turn him into a girl.
Princess Noctis. Hah.
He was gonna catch so much crap for this later.
“Noct?”
Noctis jumped slightly at the voice. He hadn’t heard anyone enter his room, still lost in thought. Not thinking, he peeked his head out of his bathroom only to be met with Ignis’ perplexed stare.
“Yeah, Ignis?” Noctis winced at the sound of his voice. It was too high pitched. Felt too much like he’d reverted through puberty or something.
“Are you alright?” He was still singing. He was actually pretty good at it too. It didn’t stop the irritation Noctis felt at the question, though.
“Alright? Do I look alright, Specs?”
Ignis paused for a moment, not sure how to answer that.
“Well, I would say you look—“
“There are a few important things missing from between my legs, Ignis. No I am not alright.”
The sympathetic glance Noctis earned in response did not help his mood.
Sighing, Ignis danced over to Noctis’ bed to sit down (and despite Noct’s ire, he found himself snorting at the display).
“Our best bet would be to wait out the cold. I will admit, all of this singing gets old.”
“You’re totally doing that on purpose.”
“Luckily for you, a bit of medicine should quell the symptoms. It seems your sneezing is the culprit of all of the—“
“Achoo!”
Something roared from outside. There was a fair amount of shouting, and Noctis was sure he’d heard a few members of the kingsglaive among the voices. He didn’t even want to know.
“…Mishaps. I’ll be taking you and,” a glance was shot at the flower pot, “Gladio back to your apartment so that you can rest up and clear up this illness. Hopefully by tomorrow, this will all be over.”
Noctis shot a look at the flowers as well. He really didn’t want to be in the same vicinity as Gladio when he changed back.
“Maybe you should take him back to his own house.”
Ignis quickly realized the implications behind Noct’s words. He sighed.
“I suppose I shall.”
Noctis was quiet for a moment, picking at the fabric of his pants and noting the odd manner in which they fit his new physique. All of his clothes were fitting weirdly. He hadn’t changed height, making him rather tall for a woman, but he had changed shape. Everything just felt…weird.
“Specs.”
“Yes, Noct?”
“What do I do if I don’t change back?”
The resulting silence was not comforting. Not at all.