Jeff's dad clicked through the options, looking at them closely before noticing the "add target" function. Clicking it he soon had a model of himself rotating slowly on the screen, with a tab showing Jeff was still also selected.
"Got something in mind, dad?"
Mike smiled sheepishly, and scratched the back of his head.
"Well, man to man...I always kinda wanted a bigger dick. Just to see what it's like."
Jeff winced, slightly embarrassed at talking about that with his dad, but watched as Mike found the appropriate option under "Body Part Transformation"
"Here we go, final form 'genitals of Mike'. I'll put it on ten inches, and for duration...let's say just the weekend. Can't wait to try this."
Mike clicked change, and both of them felt a tingle pass over them. To their surprise, the display flashed on both of their tabs, and then changed to a picture of Jeff.
Slowly, Mike pulled down his cargo pants, revealing a bulge in the jockstrap he wore underneath. Shivering slightly, he peeled that down, revealing the older man's thick, throbbing erection, short but powerful.
Oddly, Jeff did not feel disgusted by his dad getting his dick out in front of him. It even felt oddly...familiar. To his surprise, he found himself pulling off his shirt, and tugging off his socks, before dropping his pants and sliding closer to his father, naked.
"Urgh...Jeff...what's going on..."
Jeff's eyes were out of focus, and he was breathing heavily. His father could not push him away as he lowered his ass onto the throbbing cock that had created him, feeling it pierce his rear and slowly slide inside.
It was then that both of them snapped back to reality. Jeff immediately began struggling, and Mike freaked out, trying to push his son off his crotch.
"What the fuck!"
After a brief, futile struggle, Mike looked down and felt his groin. The flesh of his crotch was flowing smoothly into his son's rear, with no seam between it. In his attempt to push Jeff off him, he had wrapped his arm around him and was touching his chest, and he gradually realized that he could feel his son's flesh like it was part of his body.
Jeff was sweating, his heart pounding, until he too realized that something was off; his heartbeat in his chest was getting quieter, and he could feel another. He shivered, feeling heat passing through him, as the force of a dominant heart pumped unfamiliar blood into his body. He felt flushed, and stiff, and oddly tingly.
Jeff's groin began to ache, and he lowered his hand to feel his dick and balls shrinking, pulling inward. Whimpering, he tried to grab on as they wrenched in and vanished. He could smell his dad's body odor all around him, and as he raised one arm, he realized it was emanating from his own skin.
Mike, meanwhile, was panting, overcome by a powerful and overwhelming pleasure that was making him forget his predicament. He found himself stroking Jeff's chest up and down, raising both hands to hold his son's sides and pump them slowly.
Jeff tried to speak and protest somehow, but only gagged a little, something warm and sticky drooling from his mouth. Raising one hand, he touched slimy, clear fluid, pulling it away to stare in shock at what he recognized as precum.
His legs began to bend, then curl, pulling upward to cradle his father's balls, before tightening more, merging with the hairy orbs. He felt two weights in his lower limbs, heavy and hot, creating semen inside Jeff's lower body.
Lock by lock, his hair began to fall out, and even as he reached up to touch it, he found his arms shrinking and becoming weak, disappearing into his torso and leaving him helpless as he felt himself stiffen and slowly shrink.
Looking down, he saw his hairless skin grow huge veins, his flesh pulling up into a turtleneck below his head, which soon began to turn upward against his will. His facial features pulled in and softened, his mouth growing wide and thin, each stroke of his dad's hands on his chest making his change accelerate.
Soon, Jeff's head was no more than a throbbing, red dickhead, and yet somehow he could still see, and feel. Particularly a potent, hot pressure building beneath him, growing inevitably stronger and stronger, building to a climax, until finally with a volcanic eruption of heat and salty stickiness, Jeff spurted his father's cum all over the older man's red shirt, leaving Mike panting and overwhelmed with pleasure.
Mike lay back, still stroking his generous new cock, father and son now one.