Jeff yawned, then looking at the hour he noticed it was too late. "Maybe I should try this tomorrow" he said, allowing his body to fall on the bed and get asleep immediately, unintentionally leaving the Chronivac turned on.
Melanie slowly opened the door of his brother's room, even that she was just one year younger than Jeff being 15 years old she always loved to play pranks on him, having fun and laughing seeing her brother's annoyed reaction. That night she planned to do something to him while he was sleeping, but then she saw the bright screen of the computer in the dark and lightless room, her curiosity grew and decided to check it.
The more she read about it the more excited she was, a computer that could make any thing real? She imagined all the things she could do to annoy her older brother, then she saw what was Jeff intending to do.
"Oh, my, God, big bro was trying to turn into someone else's vagina!??" Melanie blushed but at the same time she was intrigued, she looked at her brother's bed, having his sleeping and clueless body on it, she smiled thinking on her next big prank.
"Hmmm, so big bro was getting excited to turn into a human vagina, let's see if he likes that idea applied to him!" She rewrote some of the things Jeff did, setting herself as the subject and the duration until she wanted, also modified her taste to like the things entered her mouth or expelled her mouth, only Melanie was being able to modify the things she set. Everyone would think that all of that was normal, only Jeff and Melanie knowing the truth, finally she saw the way she needed to become her big brother's vagina, only needing a connection between their two sexual organs. She clicked on save the changes and smiled about to begin with her ultimate joke.
Melanie lowered Jeff's pants and underwear, blushing looking at his big trunk, "not that he's going to keep that for now" she thought giggling, Jeff didn't realise what was happening since he was really tired and deeply asleep. Then Melanie took off all her clothes, throwing them on the floor and standing on the bed above her brother's penis, she slowly lowered her crotch until she couldn't more, grabbing the penis and shoving it inside her vagina, almost moaning feeling the warm of the big stick inside him. "Things should begin now" she giggled.
And Melanie was right, the changed occurred seconds after, her crotch and legs were completely absorbed by Jeff's, her arms shrunk until she was just a torso with a head, attached to Jeff's crotch. It seemed like she was turning into her brother's penis but was the complete opposite, as his testicles shrunk and disappeared while Melanie's body began to be absorbed even more, slowly lowering her torso until only her head was left between Jeff's legs. The transformation was finished externally, just the internal stuff was left.
Inside Jeff's anatomy there wasn't much left, as his testicles disappeared with his penis after absorbing and shrinking Melanie, just having a bladder which also vanished, as his younger sister was about to replace some of them. Most of Melanie's organs vanished too, but she was still alive thanks to the Chronivac, just leaving her womb, ovaries and reproductive tract intact, which grow until it filled Jeff's insides, making them now part of him, the vaginal track leading to the womb connected with Melanie's mouth as her stomach turned into a bladder also connected to Melanie's mouth, but with another small hole that opened inside it, the rest of her organs were gone, Melanie's transformation was finished, she was a human looking vagina in his brother's crotch, she couldn't wait to see his reaction.
The next day Jeff woke up, stretching his arms and body, when he stood up he felt something weird, he looked at the floor, seeing his sister's pajamas scattered everywhere, "what the..." Jeff said noticing that he was naked from his waist to his feet, but most importantly, he no longer had a dick, "THE FUCK!?" he yelled, just hearing his sister's laugh seconds later.
Melanie giggled, "scared? Big bro?" Jeff felt weird on his crotch, but at the same time it was pleasurable, noticing that he began to drool from his crotch.
Jeff looked further, he couldn't believe it, he rushed to his sister's room but she wasn't there, he grabbed a mirror and jumped to her bed spreading his legs and putting the mirror in front, he gasped after he looked. His younger sister's head was between his legs, she smiled.
"So, what do you think of my new look?" She kept giggling containing her laugh, every word she pronounced made Jeff trying to hold his moans, he also noticed that the inside of her mouth looked like the entrance of a vagina, he was mad, his younger sister did what he was trying to do but in himself.
"What's wrong with you!? So you saw the Chronivac! Are you crazy!?"
"You're the actual crazy, you're the one who wanted this, I was just, a little inspired~"
Jeff moaned. "God... B-but I wanted to someone else pussy, not someone becoming mine, which I didn't had!!!"
Melanie laughed again. "I know, but I guessed that it would annoy you if I did the same thing to you! Now how it feels, huh? Besides, you could learn a few things more about female anatomy you dumb"
"You know what, I'm about to undo all this nonsense!" He walked to the computer, meanwhile Melanie licked her own lips which stimulated Jeff, as he tried to change the things his annoying sister did, realising that she locked the changes entirely at her mercy, "no..." He yelled, "YOU PUSSY."
"That's what I am! Now look at this" Melanie stuck out her tongue even more, that was also a change made by her, her tongue could reach her own nose which worked as Jeff's clit. Jeff moaned trying to resist but he surrendered, Melanie's stimulation felt great for both Jeff and herself, then Jeff followed inserting two of his fingers inside Melanie's mouth, it felt really good, way more than his penis. Minutes passed and Jeff kept masturbating his new sister shaped vagina, until he couldn't hold it more and squirted, Melanie gladly vomited his brother's cum through her mouth, she loved the feeling and taste of it, licking the remaining cum of her lips.
"God, that feels sooooooo gooooood, this was better than I expected, congratulations on your first female orgasm by the way, not many can reach that" Melanie giggled, still twitching Jeff's vaginal walls as she spoke. "Also I'm not planning to leave for a good time, this place feels really comfy, why don't you try to insert a couple of toys inside me~"
"Ugh..." Jeff sighed, tired and sweating on the bed wanting end all of this to even that the experience felt really good to him.