"Kat, no," Dan begged. "Please don't turn me into an animal!"
To his surprise and relief, Kat considered for a moment, then said, "Okay!" She lowered the wand and Dan felt the strange sensation subside. Kat turned to a different page of the book and smirked, "I have a way better idea anyway."
Dan heard Kat recite something different and point the wand at him again, and a different, more intense tingling sensation ran through him. "Wha- what's this?" he asked.
"Put it this way- you're not the only sibling who likes girls," Kat replied cryptically.
The air shimmered around Dan and all of a sudden the boy was naked. He blushed and raced to cover his crotch, only to get a weird trippy vision of a sperm fertilizing an egg. Once he returned to looking at Kat, he asked, "Tell me what's going on, damnit!"
"I saw your search history a while back," the young woman explained teasingly. "You always like looking at stuff with two girls. I'm into girls and guys alike, but I've always wanted to get with a girl. So I figured, why not scramble your DNA and turn you into a girl I can have my way with?"
The tingling seemed to get stronger and ripple through Dan's body. "K-Kat," he stammered, gasping with pleasure, "That's impo-ohh..."
"Oh, with magic anything is possible," Kat countered. "Your body is already starting to cross over to the other side. But don't worry, I can give you a nice simple sex education lesson as you go!"
First off, Dan felt his skin seem to prickle all over, and it became almost devoid of hair. "So, first off women obviously have less thick body hair than men. But don't worry, I think you look prettier like this! Especially your chest, it's so smooth now," he heard Kat taunting.
His skin seemed to prickle still more, and he screwed his eyes shut and then opened them after a moment. "Speaking of smooth, your skin's also gonna get less rough and more soft. You've got a way prettier face like this, too! I just wanna smoosh those cheeks and kiss those full lips!" It surprised him how genuine Kat's attraction to his emergent body was.
Next came a mix of tightening and loosening sensations, as parts of him tensed up while others seemed to flare out. "Now your proportions are adapting to be more girly!" Kat said. "Say goodbye to wide shoulders and hello to a thigh gap and bubble butt!" Much as he hated to admit it, Dan did kinda feel like this new body was... kinda sexy. His petite hands and feet seemed way more lithe and subtle.
The tension moved to his throat and he swallowed so hard it felt like his neck tightened up. "Wha-" he began, only to realize how much higher-pitched his voice had gotten.
"Oh yeah, I just un-broke your voice too," laughed Kat. "I think it's way cuter like this anyway."
Even though most of him had changed now, anticipation only continued to build and hormones continued to surge in Dan's body, and he felt a bit confused why until he realized what about him hadn't changed. "This is the really fun part," Kat purred, licking her lips. "When this is done, you'll totally have gone from male to female."
The tension first emerged at Dan's chest, and his nipples got hard- and slowly began to swell. "See, when you start developing into a man your body releases hormones that stop you developing breasts. Without them, you're gonna get big, soft boobs," Kat explained with satisfaction. Sure enough, under the puffy nipples flesh was accumulating as Dan formed mammaries, which soon swelled to pert, sensitive C-cups. "You've got some nice tits on you!" he heard Kat comment as he tried to hold the soft, jiggly flesh steady only to feel the tingling sensation get more intense.
Kat's eyes darted down to Dan's crotch, and his own followed. They both saw his erection standing up eagerly, and Kat looked at Dan and smiled evilly. "The other thing the hormones do is tell you to form a penis and testicles," she explained. "Now you don't have them, you'll develop a vagina and ovaries."
Dan yelped in his heightened voice as this process reversed, amazed at the fact that it felt pleasurable instead of hurting. His balls slid up inside him and he felt himself get castrated as they reshaped into ovaries, and his penis seemed to shrink without his erection dying down. "Without masculine hormones to make you form a penis, instead you're gonna have a clitoris," purred Kat. "And your scrotum is about to tuck in and peel into a vaginal slit that links to a womb inside you."
Sure enough, Dan felt his cock recede more and more until only a tiny, sensitive nub remained, and felt his body open out down there, while in his crotch formed a large space linked to his ovaries.
He? She, Dan realized. She was a girl now. And to her surprise, she realized she wasn't Kat's sister, or even related to her in any way. To her embarassment, she found the girl standing before her hot, and her body responded accordingly. Her body began leaking female juices and her nipples and clitoris became hard.
Not only had Dan gone from a young man to a young woman, she was now Kat's plaything...