You were getting tired of being mistaken for a boy, so you wanted to be something highly feminine; but you didn't want to be something with a beastly or overly sexual side, either. You chose the one thing on this list that fit the bill "I want to be a fairy!" You said.
"Excellent choice!" The headmistress said as she started to write down information on the form. "I myself chose that when I first came here almost 80 years ago, and I've never come to regret it."
"You're over 80!?" You said. "...and a fairy?!"
"Like I said..." The headmistress started before beginning to shrink down, climbing onto the desk as she does. Her ears grow large and pointed, antennae sprout from her forehead and large butterfly wings flare out from her back; translucent and colorful, like stained glass. "You can retain a human form with practice. We generally like to do so when greeting ordinary humans who apply here in order to put them more at ease, isn't that right, Amitiel?" She said, glaring at the angel with larger, more solid colored eyes, her arms folded.
"Huh?" He looked over his shoulder. "Oh, sorry Headmistress Falla, you know I forget they're there sometimes."
"Besides, fairies start to age much slower than humans starting... right around your age, in fact." Falla returned to her human state and filed away the paperwork. "Amitiel, have someone come take Ms. Archer's belongings to the fairy dorms, I'll personally see to her transformation." The headmistress started to lead you down the hall. "Now, your clothing and possessions will have to be altered to accommodate your imminent fairy form, but you'll be able to change them back when you've mastered turning human."
She lead you to what appeared to be a science lab, but rather than chemicals and formulas on display, there were potions and spells. Within was a red-headed man with pointed ears about four feet tall wearing a green lab coat. "Top o' the mornin' to ya, Mrs. Falla; would this be the new student?"
"That she is Noben." The headmistress said.
"Hi, I'm Riley Archer." You said to the lab-coated leprechaun.
"Pleased t' meet ya; an' what manner of creature did ya choose t' be."
"A fairy."
"Ah, I see. Jus' like our own headmistress." Noben took a key and unlocked a cupboard before waving a hand across the door, a magic circle glowing for a brief instant before it dissolved. He then opened the door. "Y'know, she be the first human born t' lead this place." the small man said as he was rooting around inside before taking out a tiny jar of golden dust.
"Stop, you're embarrassing me." Mrs. Falla said with a blush.
Mr. Noben handed the jar to Mrs. Falla. "It's just about lunchtime, so I'll be headin' out."
"Thanks, take care." The headmistress said to the departing leprechaun. "Now, just to make sure you understand, once this change takes place, there's no going back or choosing something else. Not even shapeshifting will ever change this fact. You will be a fairy forever."
"I understand." You said. As she unscrewed the jar you ask. "Is this going to hurt?"
"I'd call it, for lack of a better phrase, intense." She poured the golden dust into her hand and blew it onto you. It suddenly stopped and hung in midair as Mrs. Falla produced a star-tipped wand from thin air and waved it at you.
A magic circle appeared under your feet patterned in many floral designs and elegant script, the golden dust started swirling around you like a glittering tornado and you were lifted into the air. An electric sensation coursed through your body, you could feel your body shrinking, though your ears and eyes were not keeping up quite the same pace, just as Mrs. Falla's features had indicated. The legs of your jeans split into sections, turned pink and fell into a shape like a flower petal skirt while remaining the same denim material. Your shirt turned green and tightened up as it took the shape of leaves crossing over your chest, and opening up in the back. Your ears now felt like they were being pulled outward as they took a long, pointed shape. Antennae grew from your forehead as your back felt like someone was kneading your muscled like bread dough. Pressure built up on your back. You took a deep breath and strained as four small protrusions pushed out. A huge burning jolt of a sensation shot out from your back and with a fearsome shout, four beautiful fairy wings burst into existence.
You remain suspended in midair, but now it's by the power of your own wings. The feeling is thrilling.
"Come," the headmistress said, "let's get you to your room."