Dina smiled and looked at the others.
"I choose Lissi to be my mate."
"What?" said Lissi, clearly surprised by the decision. Everyone else was surprised too, and they watched as Lissi began to moan in pleasure. Her hand traveled down into her pants and she began to masturbate.
Her moans slowly began to sound deeper, becoming a man's voice. Her body began to gain muscle mass as her breasts shrunk to be replaced by pectoral muscles. Her legs began to fuse together and ripped her pants off, revealing that she was pumping a dick that was quickly growing larger.
Her, now his, legs continued to fuse, quickly being covered in dark blue scales. His feet flattened and became a single flipper. His dick had stopped growing, and it was now almost 2 feet long!
A large spurt of cum shot out of the end of his cock, which slowly became soft and was pulled back into a small slit in his scales.
His body was now very masculine and muscular. He easily pulled himself over to where Dina was laying and he kissed her passionatly. The two of them began to make-out with each other and they rolled back into the small pool of water, which promptly grew to accomodate the extra person.
Lissi, now Larry, was violently rubbing Dina's large breasts, and she had her hands on his cock, and was swiftly pumping it back to attention. It became fully erect again, and Dina cried out in joy at its immense size. She practically threw herself onto it and the two mated wildly for almost an hour.
Larry finally came in her, filling her vagina with his hot seed. Dina let out a scream of lust as she orgasmed with him. Unknown to both of them, mermen's seed had a magical effect, and whenever a female had sex with a merman and he came in her, they female would become even sexier.
Because of this, Dina's scream of ecxstasy turned into a moan of new arrousal as her breasts grew again, becoming perfectly round G cups, and her waist thinned a little bit, while her hair grew longer and softer. Her lips became fuller and her vagina grew larger.
This caused Larry's dick to also grow, because he was her perfect mate. His dick was now an amazing 2 feet and 10 inches!
The two surfaced and resumed the game, kissing each other every now and then. Dina's fingers wandered to her vagina and she gently pleasured herself while the others continued the game.