"Stop this right now!" you start to say, only to have Kevin lean back and laugh. The shudders from his laughter make you wobble around dizzyingly until you feel queasy.The kevin-quake gradually subsides, with only an occasional tremor, and then he leans over to look at you agin.
"What exactly," he says, tone flat and unamused, "are you going to do about it if I don't?"
You feel the change spread up your still-human torso, and you look down at yourself in horror.Your abs vanish, replaced by a large, blue vein. Your chest starts going the same way, and you realise that the tickling sensation in your shoulders is your arms being absorbed into Kevin's dick. You look up, mouth open to say the words that might stop this, but it's too late. The last thing you see before your upper body and head are swallowed by his newly formed foreskin is the angry glint in Kevin's eye.
He shudder and grunts while you're in the dark, and you feel a new swell of pleasurable sensation. Then the darkness bursts and you see again. you try to move, to open your mouth, but only a large bubble of precum forms at your lips. You're mystified for a moment, until Kevin walks, stark bollock naked, over to a full length mirror, puts his hands on his muscular sides and proudly displays his new, pleasurably throbbing, dick to you.
You stare. You can't help it, since you can't blink or look away. you get a moment's relief as Kevin swings his hips from side to side, obviously approving of what he sees, and then faces forward again.
"Bit fatter in the head than my old one.." He reaches down and you see him heft his new ballsack. You feel his fingers gently probing the testicles that are inside. "Bigger balls too. I suppose I can get rid of this now," and he rubs the marker that spelled out his name from the top of his foreskin.
Immediately, you shudder and the throbbing in your body gets harder. The pulse from Kevin's body gets stronger, more pleasurable, and you see Kevin thrust his hips forward. For a moment you're not sure what's happening, and then you feel something familiar happening in Kevin's balls. Suddenly your flanks are heaving with muscular contractions, and great gobs of white cum are flying from what was recently your mouth. Through the horror, you notice that Kevin's abs are flexing and his hips are thrusting, and you have a quiet hope that this isn't pleasant for him.
Finally, the spasms stop, and a few final blobs of cum dribble from your mouth. You hear Kevin sigh as you shrink and his foreskin swallows you up.
"I... really hope they're all like that," he says, with a hint of awe.