...a mermaid. Not only that, but the mermaid looked really hot to Daryn. It was so nicely detailed, with an eloquent tail, scales that sparkled like sequins, gorgeous flowing hair, an absurdly pretty smile, and big bared breasts. Daryn smiled pervily, closed the book and put it to one side. He'd have to check this out- that mermaid would be so nice to beat off to tonight.
That night, he checked out the book, sneaked it home, waited until everyone had gone to bed and pulled out the book. He got the page with the illustration of the beautiful mermaid in one hand and his penis in the other, slowly stroking himself and imagining cumming all over her soft tits. But slowly he lost focus on her chest, and found his eyes drawn to the rest of the scene- how much fun she seemed to be having swimming in the sea, and her long flexible fish tail. Slowly he grew less aroused by her body and more enraptured with her life.
It looked fun to be a mermaid. Daryn had a crazy idea- there was a lake near his house, and he had a really intense urge to go swimming. He sneaked out of his window, still holding the book like a lucky charm, and walked to the lake quietly in the dead of night. Once he reached it, he lay the book down and undressed. His T-shirt was thrown to the ground and his shoes, socks and pants were removed too. He would normally keep his boxers on, but something about the mermaid fantasy made him want to do this naked, so he pulled them off too, wading into the lake naked and slowly starting to swim.
At first swimming felt difficult, but it rapidly grew easier. He felt his muscles and figure turn more slim and lithe and streamlined, and loved how much more comfortable it made swimming. Soon a technique he hadn't considered came to him- keep his legs together rather than separating out their motions. He pressed them together, and they seemed to become one. They felt more natural this way, especially as they became flecked with scales and his feet reshaped into tailfins.
It felt so natural and comfortable to swim now, and he felt closer to being that beautiful mermaid girl than ever. As he realized that, he also realized something that confused him. He had had something between his legs before they fused into a tail. His penis, where was his penis?
Nowhere, he realized. Now he had eggs inside him to get fertilized. And speaking of which, when she got bred, she'd need to feed her young. Upon that realization, her chest began to sprout breasts- first his nipples widened and grew sensitive, and then soft mounds of flesh emerged around them, until she had prominent mammaries just like her counterpart from the book.
Daryn looked at her reflection in the water and gasped. She had changed from a human boy to a beautiful mermaid!