As Kara rode Milo toward climax, she felt a crawling sensation up her sides. Looking down she could see the scales from her legs rapidly spreading up her torso. Something compelled her to wrap her legs around Milo and lean back. She did so, with her hands on Milo's shoulders. Now almost perpendicular to his torso, her legs began instinctively to slowly tighten their grip around her lover. Yet Kara could also tell something was wrong; her legs no longer felt right. Then through the bubbling and churning water she saw why, as the tentacles that had been her legs became visible as they wrapped around Milo's torso and legs.
Kara opened her mouth to say something, to alert Milo. Before she could, her orgasm hit. Kara threw her head back and screamed out in pleasure. With the orgasm, her tentacles abruptly tightened their grip and that caused Milo to climax. Kara felt her mate's seed pumping deep into her, the tight grip ensuring none would escape. Kara had never been loud during sex, but the orgasms brought on by her transformation were so forceful she couldn't help it.
When Milo stilled within her, Kara's own orgasms subsided and her grip loosened then released. She fell back from Milo's lap into the deeper center of the hot tub and looked at what she'd become. The scales her up to her shoulders now and working their way down her arms. Kara's skin began to itch and she soon found herself scratching her torso and the six tentacles that had previously been two human legs. Her skin felt like it was cracking open and the scales began to break up, revealing dark, rubbery skin beneath. She had been expecting some version of a fish tail, but Kara realized she was becoming some kind of octopus mermaid instead.
"Oh, Milo, I'm becoming some kind of monstrous thing like Ursula."
Milo gently grabbed Kara and pulled her into his arms.
"You're no monster" he reassured her. "You're beautiful and I love you."
Milo held Kara's hands, but the scales working their way down her arms soon reached her digits and he found himself unable to grasp her fingers any longer. Minutes later, her last two rubbery tentacles had formed, in place of what had been her arms. Kara began to cry at the loss of her hands as Milo did his best to comfort her.
Distracted as he was with Kara's changes, Milo paid little notice to the scales now covering his legs. His new form was about to be revealed.