You might be wondering "What's Fantasi" and it's literally a drug I made up for this dumb idea I had but I may use it again as some point cos caps are all about plot devices
Mike could barely contain his excitement as his girlfriend Eva had blindfolded him and lead him to the bedroom the moment he came home from work. Things had been feeling vanilla for a while, and she'd obviously taken the initiative.
She got close and whispered "Think of your biggest fantasy, and open your mouth"
Their boring sex life had driven to Mike's mind to strange places recently. Elaborate and bizarre scenarios. So when she said that, he thought of one of his weirder ones. And then something was pushed into his open mouth, and quickly dissolved on his tongue
He recoiled in surprise, and pulled off the blindfold.
"What the hell was that? Have you drugged me?" He asked
Eva had a gleaming smile on her face when she said "It was that new thing, the Fantasi drug, it makes your fantasies come true"
Mike's face fell. He had heard of it, he knew it worked, and he knew what was coming.
He tried to stay stoic as his eye began shrinking, his bones reforming as he shrunk in height. Eva stared down at him, obviously too focused on his changes to notice her own. Darker skin, dyed hair, her natural breasts replaced with real ones. The changes slowly working down her body
"Wha-" Eva felt like something was caught in her throat, her voice sounded wrong, a little too dep. She tried coughing and ask again "What's ha-" This time it was even deeper than before
"I'm sorry honey, you should've warned me. It's... it's just a stupid crazy fantasy but I..."
"What's going to happen to us?" Eva managed to get the whole sentence out, only now beginning to notice her fake tits, and larger hands
Mike was forced to crane his neck upwards to make eye contact with his girlfriend now. He was just under eye level with her crotch
"I thought about how hot it'd be to be... to be super short. Like. 3 feet tall."
"And... me?"
"You'd be my trans girlfriend... willing to dump loads into my mouth"
Eva's jaw dropped. She expected to get some bigger tits, maybe gain a few pounds. Not... not this. The final wave of the change occurred, and she moaned as her dress was pushed aside by a new addition.
She let out a grunt, her vocal chords changing her exclamations of pleasure, and tugged her cock. The feeling was like nothing she'd had before. She finally made eye contact with her boyfriend. He looked so pathetic. Tiny, his muscles had deflated, and he was eyeing her cock with an eagerness.
"Oh" She said with a devlish grin "Does this excite you?"
Mike could simply eagerly nod
"Then open up wide"
He eagerly waddled under his girlfriends new cock, and waited for the climax
As he swallowed the salty cum, a new experience, he felt almost a euphoria. He expected it to be followed with an erection, but he noticed his cock stayed completely limp, simply dripping precum onto the carpet.
A couple more times the scene repeated that night, Mike unable to get erect, Eva rarely staying soft for long, and they happily fell asleep.
Both were initially shocked, but by the end of the night had greatly enjoyed Fantasi, and decided to use it again in future. It should pass after 8 hours.
However Mike was shocked when he woke up to the grunting that had become all too familiar the night before
"Good morning baby" He heard, and opened his eyes just in time to see the finish. However while the night before, he had found it so sexy, this time he gagged as the splatter of cum hit his face
The mental aspects of the Fantasi had passed, but for some reason their bodies hadn't returned to normal.
They called the company, and got brought in for tests, and got the terrible news.
"I'm afraid your... unique fantasy has caused an issue we've never run into. We cannot reverse the physical changes."
Both were horrified, however Mike would take it far worse. Barely 3 feet tall, a non-working cock, and a girlfriend who despite the passing of the mental change of Fantasi, was still eager to cum all over him.
He hoped that would pass, but he kept waking up to her jerking it. Sometimes he'd walk into the bathroom to find she'd got there first, ready and waiting
"Please, honey, we don-"
"Well... you did this to me Mike. I will never get my vagina back. I'll never get my boyfriend's hot body and working cock back. You owe me the other half of the fantasy"
Mike looked down, ashamed. For some reason this seemed to turn on Eva even harder. Her tastes were changing daily since change. Everything seemed to be getting her turned on.
And as the tent fully formed in another dress, Mike waddled over, and Eva got ready to feed him, and he prayed Fantasi would discover a fix soon