Jeff, now in the body of her 11-year-old sister Kara, scurried her little body across the hall, marvelling at her new diminutive height.
She opened the door to her bedroom and saw her "big brother" still asleep. She stood next to the bed and slowly prodded at the 16-year-old boy's shoulders. It was unbelievably surreal to be seeing and touching her own face like this.
Kara began to stir. Jeff started to whisper. "Hey, Kara, I have something exciting to show you." Kara suddenly woke up, startled, looking deeply confused. Kara began to stretch, then threw back the sheets, and saw the tall, 16-year-old, shirtless, unmistakably male body lying in the bed. Then the new teenage boy noticed the 11-year-old girl with beautiful blue eyes starting at him. The puzzle pieces quickly fell into place. Kara was in Jeff's room, in Jeff's body. How was this possible?
"What did you do to me?" Kara finally managed to murmur.
Jeff grinned. "It's not permanent, don't worry. I switched our bodies. It's called the Chronivac. Let's enjoy this for now and I'll explain later. If you don't like it, we can switch back, I promise."
That was enough for Kara to process the shock. While Kara knew this was a completely disgusting situation, he had to admit that being a tall, strong boy was a fantasy he had always had, and had never thought possible. Kara swung his long legs and big feet to the ground, and awkwardly sat up, running a strong male hand over his new torso. "This feels so weird..." Kara touched his face, marveling at the angular, handsome boy face that had replaced his weak, soft, innocent girl face. He was too excited to question what was going on or how it was possible.
Kara stood up carefully, marvelling at his new height of 6'1". Being this tall was an absolute gift and a privilege which never would've been possible as a pretty, weak girl. Kara was thrilled and walked his long legs over to the mirror.
There was Jeff, alright. Jeff's handsome, stupid face, Jeff's long, powerful, slightly hairy legs. Jeff's muscles.
"I'm... a boy," muttered Kara. "I'm a boy!!"
Jeff grinned from her little girl's body, the body she had always wanted. "You're a boy!"
Kara looked at his long legs and his strong, lean torso. "So I get to be you? You're stuck as a weak little female? Why would you want this?"
Jeff was a little embarrassed, thinking of her new, weak little female body. She didn't have a good answer, but this is what she had ways wanted. "Just have fun, man."
"Man." Kara surveyed how good he looked, mostly naked with just a pair of black boxers shorts. "So, I have your.... uh, thing?" He pulled his shorts down to his feet. "Woah!"
There between Kara's legs were the disgusting male parts he had always been so fascinated by. Kara's penis... his cock. "It's huge!" grinned the new teenage boy.
"It's not huge, really, just pretty normal for your age..." mumbled the little girl Jeff.
Kara was mostly ignoring her. "I have a penis!!" Kara moved a hand toward his limp, floppy organ, letting it flick back and forth just a little. He was in absolute ecstacy.
Kara had seen Jeff naked growing up as kids, but never really thought about it. As she got older, she became very interested in anatomy, knowing that she had been robbed of the male parts that would've granted her tremendous privilege. Instead, she had been cursed with female parts, which would grant her nothing but helplessness and excruciating pain forever.
Suddenly the tables had completely turned. Kara was a boy now. A "He" now. Behind his dangling weiner was a gross, slightly hairy bag of flesh, safely containing two testicles. Kara only had a vague understanding of anatomy, but knew that boys had balls between their legs. "These are my balls! I have balls! I'm a boy!!"
Jeff felt weird looking at her own junk, but was pretty happy knowing that Kara was satisfied. "You are a boy! Have fun with your dick and balls, because I don't have any."
Kara noticed his "little sister" looking embarrassed. "What's wrong, little sister? Are you upset that you don't have a dick like I do?" Kara turned to Jeff and made sure the soft organ bounced back and forth a little.
Jeff didn't know how to react, but loved the role-playing. "I'm a girl, Kara! Don't make fun of me. You know girls don't have penises. Girls can never have penises, only boys. Girls are born with vulvas instead. We have to learn to love it."
Kara chuckled with his male voice. "Love it? What do you mean? How could you love being a weak little thing forever? How could you love not having a penis? Having a penis is amazing. Having balls is amazing. Us boys have everything we want. We can play with our dicks any time we want. Watch." Kara took his skinny flaccid penis in his hand and flopped it around. He then took a hand and lightly tapped his ballsack.
Jeff kept playing around. "I know having a penis is fun, but us girls don't have any choice. Girls have a vagina. Look." She pulled her panties down, exposing her vulva, the vertical slit that marked her as a female. "This is my vulva, and I have to live with this between my legs. Because I wasn't born a boy, I can never dream of having a cock, never dream of having balls. It's embarrassing but there's nothing I can do about it."
Kara was so excited to hear his little sister play along. He rubbed his penis head through his foreskin, rubbed his testicles through his scrotum, and touched his butt for just a moment. Now was the time to enjoy this as much as possible.