Xavier's grunts of pain and pleasure were muffled by the giant dick that was filling his mouth. He reached forward, grabbing his father's powerful hips, holding on to the man's muscular lower body for support as he was roughly taken from both ends. His field of vision was utterly filled by the monstrous brute his father had become: powerful abs tensing with every thrust of his sire's powerful tool, the muscle visible even under the hair that ran across his father's powerful stomach. Xavier couldn't begin to imagine how his father had become so massive; he could think of nothing else. His own dick was rock hard, leaking pre onto the floor as he experienced his first time being fucked from either end.
Xavier tried to look up, to see his father's face. But all he could see was a pair of immense pecs, jutting out of that hairy torso, covered in fur. His mind consumed by muscle and cock, Xavier didn't notice at first as he began to change. His dick became longer and harder, his balls swelled, pumping out more cum, sending testosterone flowing through him. His muscles hardened, then began to expand, pulses of growth racing through them in time with the thrusts of the giant cock in his mouth.
"That's it, boy, grow for daddy," the huge man in front of Xavier growled, thrusting his dick harder, forcing it deeper down the growing freshman's throat. Xavier began to grow faster, his body becoming taller and broader, more muscle racing to fill the newly-available space. Behind him, Adam grunted excitedly, finding the skinny ass he was fucking suddenly blossoming with firm muscle. He smacked Xavier's glutes approvingly, hooting encouragement at his brother.
Xavier pulled his hands away from his father's hips, and grabbed the huge man's balls instead, one in each hand. He squeezed them slowly, teasing them, and was rewarded by a bellow of lust from the giant man, who then began violently fucking Xavier's face, thrusting away with a level of desire that bordered on rage. Xavier squeezed his glutes around Adam's dick, and was rewarded by a gasp followed by faster, rougher fucking of his growing ass. Xavier's body grew even more dramatically, his muscles bulging spectacularly, growing nonstop.
Adam was the first to cum, his dick exploding inside Xavier's muscular ass. Adam pulled out, his cock still shooting, sending cum flying over Xavier's lower back, glutes, and thighs. As Adam staggered away, the second explosion came, as their father sent his load rocketing down Xavier's throat. The big man did not pull out; his entire body tensed up, every muscle on glorious display, as his throbbing tool filled his son's gut with cream. Xavier's physique drank it up, his muscles ballooning dramatically.
Xavier pushed himself off of his father's dick, then stood upright. His head swam for a moment, and he struggled not to lose consciousness. His head cleared, and he watched as he father stepped back, grinning madly at him.
Xavier turned to walk away, and nearly tripped over his own feet. His thighs rubbed together in a way he wasn't used to, and his big dick bobbed out from his hips, huge and hard, leaking pre once again. He staggered over toward a large mirror, eyes widening. He was enormous. While certainly not as big as his father, he was at least half again as big as Adam. Xavier's jaw dropped as he looked at himself, taking in his monstrous, 450-pound muscleman physique. "Oh fuck..." he gasped, his voice deeper than before, hardly able to believe what he was seeing.