Caroline rode Danny hard while making out with him. It didn't take long for him to climax, and Caroline held Danny tight as he did. As Danny pumped into her, Caroline began to orgasm. She clung tightly to Danny even as her back began to arch involuntarily and she had to bite her lip to keep from screaming. Danny finished but Caroline's orgasms continued as she slid off of him. The orgasms continued and her legs spasmed uncontrolably, nearly kicking Danny as she flailed.
"Are you okay?" he asked, worried she was having some kind of seizure. Caroline couldn't responsible.
Caroline's writhing legs began to merge into a single appendage: a tail. Dark blue scales began to form across her new tail as her feet flatted into lighter blue fins. Danny watched it all with astonishment. He felt simultaneously exhilarated and exhausted, and a little strange. He managed to get to his feet and take Caroline in his arms, holding her as her changes and the accompanying orgasms subsided.
As Caroline's racing heart began to slow back down, she slowly regained a sense of where she was after several minutes completely lost in the disorienting waves of pleasure. She felt different and looked at her legs, finding her new blue tail.
She heard the young man's voice in her ear ask again: "Are you okay?"
"I...think so..." she answered as best she could. "I'm a mermaid?" she asked rhetorically. She didn't understand why, but thinking back over the day it started to make sense: her encounter in the shower at work, the behavior of people a the bar, her urge to skinny-dip.
"You haven't been a mermaid before?" asked Danny. He realized it sounded like a stupid question, but considering he didn't think mermaids were real until now maybe it wasn't.
"This is...new" answered Caroline. She turned in Danny's arms to look him in the eyes. "I swear I didn't know this would happen. Not that I'm complaining. This feels pretty good, actually. To say nothing of the mindblowing orgasm while I was transforming."
"Oh, that's what was going on" said Danny.
"Don't expect that every time you have sex" Caroline said with a wry smile. Then, as a thank you, she kissed him again.
As their lips parted, Caroline's hand brushed across Danny's chest and he let out a soft moan. They exchanged a concerned look. Danny brought his hands up to his chest. Was his chest...bigger? He tentatively cupped his chest and felt a pleasurable tingling sensation. With each breath Danny's breasts seemed to slowly expand.
"What's happening to me?" asked a worried Danny.
Caroline moved a hand to Danny's crotch and found he was definitely shrinking there as his chest grew. Panicked thoughts raced through Caroline's mind: had her liaison with this young man caused him to transform into a woman as she had turned into a mermaid? Would he become a mermaid too?
"I'm sorry..." said Caroline.
Danny's shock at his changes began to slowly shift toward pleasure as he fondled his swelling titflesh. Caroline though Danny looked kind of nice with breasts and his lengthening dark hair. Watching him , she began to feel warmth in her groin. Her hand slid down her own body and into her vagina, only to find unexpected resistance as she tried to finger herself. Caroline backed away in the Jacuzzi, trying to figure out what was going on. She was feeling so horny she wanted to fuck Danny again, but it felt different that when she had first seen him from the pool. Her body was tingling and it felt like something was coming out of her. Then the startling revelation hit her: Danny was turning from a man to a woman and she was turning from a mermaid to a merman. She glanced down at her chest, which seemed no smaller. Was a merman just a mermaid with a penis?
Caroline felt her new erect cock swelling into her hand, having grow out of her vagina. She stroked her sensitive new member. Caroline desperately wanted to put it into Danny. She swam back across the Jacuzzi to him where he was still fondling his breasts, now D-cups, his eyes closed and his head back as soft moans escaped his lips. Caroline's hand went to Danny's crotch and found his penis was gone entirely, withdrawn into a vagina. Caroline's index finger gently rubbed Danny's new lower lips. Danny opened his eyes and gazed into Caroline's.
"Please..." Danny softly begged.
Danny was fully in the throes of the mermaid virus now, enraptured by the sensations of his transformed body and wanting Caroline to fill him. Danny wrapped his legs around Caroline's tail as Caroline slid her penis into Danny's vagina. They began making out again, sinking to the bottom of the Jacuzzi, thrusting together, building toward a climax where Danny's orgasm would complete his transformation into a mermaid.