"Oh god," Kevin moaned, as the changes spread up his legs. The skin grew tougher, and long hairs grew out. He doubled over in pain, and felt his penis starting to inch up. He tore his pants away from his body, and gasped in horror when he saw that his cock was slowly growing up his body.
A hairy sheath encased his shaft, and an equally hairy sack covered his testicles. Meanwhile, Mary's own genitals become aroused by the sights and smells in the other room. Kevin has started exuding a very piggy scent, and his penis is dripping precum onto the carpet. Mary shoves a hoof into her snatch, and starts vigorously pumping her own cock. As she masturbating gets rougher and rougher, she starts squealing.
Kevin hears this, and for a moment is distracted from his own transformation. His legs shake as he tries to walk toward the sound. His scrotum is heavy and full, rubbing against his hairy thighs. He stops when a new pressure builds over his ass. Soon enough he has a pig tail, and his butt has gained quite a bit of mass. Kevin looks at his transformed body. For some reason he's turned on by the sight of his new pig bits. And the enticing sounds from the next room aren't helping kill his erection.
"Is someone there?" he called out, his voice getting higher as his changes continue. Mary stops her self pleasure for a moment. She snorts in the musky air, the smell of her own cunt and Kevin's porky aroma mixing. She can't wait any longer, and she reveals herself to him.
"What the fuck, who the... what the..." Kevin is unable to form a complete sentence when the shemale pig steps out from around the corner. More importantly, his pig dick springs to life, and gains a distinct twist to it. The tip narrows, and spews cum everywhere. Kevin's balls pull tight, and he bellows as he released his first pig load.
As he does, his nose turns up, and his hair melts away. His shirt if torn as his body expands. New pig fur travels up, coating him just like Mary. As he extends a hand down to touch himself, he finds his hands have finished changing. With clumsy hoof-hands, he strokes his shaft until it rises again. He ears are tugged out as he tugs his meat. The air becomes heavy, with sweat and the smell of sex.
"Come here you sexy beast." Mary said. Kevin, in the midst of his own lust, recognizes Mary's voice. But all that his mind registers is a sow asking to be rutted.
On all fours, he walks up to her. Mary gets down on her hooves as well, and then turns around to present her sow vagina to him. It's dripping, and pulsing in and out of her lips. Kevin sticks his snout in, and snorts. The air tickles Mary's cunt, and she oinks in pleasure. She lifts her ass up higher, and her teats rub against the floor. Kevin lifts himself up on top of her, and rams his penis inside.
The two thrust back and forth against each other. Mary's own balls hitting Kevin's, and her nipples being teased as she rubs herself against the carpet. She slides a hoof down to massage her own meat. Kevin snorts in pleasure, and lays on top of Mary so he can fondle her teats. His hoof finds a teats, and he tugs it down until milk squirts out.
That's all it takes for Mary, and she cums. Her penis expels copious amounts of piggy semen all over the floor, and over her breasts. Behind her, her pig snatch clamps down on Kevin's own prick, causing him to blow a load into Mary. Her pussy soaks up as much as it can, but spunk still leaks from her hole. The two pigs fall to the floor, rolling themselves in the puddles of cum.
Mary moves so that she's face to face (maybe snout to snout?) with Kevin. The two nuzzle each other, and cuddle. Mary's teats press against Kevin's cock, and soon both are ready for round two.