"One thing you can do," said Monica, "is to stop mocking my tits. They're real."
"They weren't a birthday gift from your mom?" asked Lydia.
"Only if you mean genetics" explained Monica. Then she took off her blouse, revealing her pert breasts and hard nipples. She wasn't wearing a bra; she didn't need one. "Puberty kicked in and bam. The tail I can make come and go, but the tits are permanent. But you're right that they're a drag for swimming."
Monica noticed Lydia was still looking at her with some skepticism. "Go ahead and feel it and you'll see I'm telling the truth."
Lydia slowly reached over and felt Monica's breast. It certainly felt real. Lydia realized she had never grabbed another girl's breast before.
"You can feel both of them if you want to be sure" offered Monica, suggestively.
Lydia pulled back, realizing Monica was enjoying it. Lydia's hand accidentally brushed the front of Monica's skirt, and felt something surprising.
"Are you hitting on me?" asked Lydia. "And do you have..."
Monica unfastened her skirt and cast it aside, revealing the teal scales of her mermaid tail up past her hips. Lydia had to admit Monica had a fantastic body that any guy would would want. Except for the one thing she had that most mermaids didn't.
Lydia couldn't help but stare in disbelief at Monica's big cock.
"I can have any guy I want," said Monica. "As long I keep my legs. I have a rare condition among naturally transforming mermaids: my human form and my mer form aren't the same biological sex. I love having guys pound my human pussy. But I've waited so long to fuck as a mermaid. And when I saw you laying here on the tile with a mermaid tail it was all I could do to resist ripping all my clothes off and transforming immediately. Please me fuck you."