Xavier groans lowly as his hands roughly glide against his giant muscled body. The 18 year old couldn't believe the sheer size that he was now. He smirked as he squeezed his fist and watched the vein snaking down his arm bloat with blood, a river snaking underneath the surface of his skin. His hands moved to touch his titanic pecs, the thickly muscled chest overburdened with so much new mass, his pert nipples now pointed downwards. Thick curls of hair sprouted from his skin, the huge stud shuddering as his giant hands rolled over them, feeling the new hairs pull against his taut skin. The new beast brought both his arms up, his giant cock bouncing up as he drank in the sight of his new physique. The head of his cock, now easily the size of an apple, pressed rather insistently into the bottom of his muscular pec-shelf, drooling a cascade of fresh pre-seed that mixed with his recent ejaculate.
Xavier always wondered what it'd be like if he were bigger. Like Adam, he wasn't exactly what the boys, well, in his case, girls, were after. Despite having different sexual orientations, Xavier didn't look the part, most people had assumed he was gay like his brother, and thus, he was painfully single. Well, that sure would change now. He smirked as he brought a hand up to feel his chiseled jawline, his hands rubbing against the grain of his stubbled beard. His features had sharpened, his visage radiating masculine, animal hunger. "Damn, I'm sexy," he murmured. The flow coming out of his huge cock grew, a river of pre-seed spewing out of the softball-sized cockhead that adorned his prodigious length. He needed to fuck something. And as he spun around, he knew just who.
Xavier knew he wasn't gay, knew he'd never fantasized about doing anything with a guy. But the sheer amount of testosterone coursing through his veins made him see everything as a target for his enormous horsecock. And who better to fuck than the guy who took his virginity? The bigger brother squared off with his lesser twin. He pushed his arms down and threw himself into a manic 'most muscular' pose, his body exploding as he flexed every muscle he had, his 450 pounds bloating off his huge frame, dwarfing a muscular hunk 200 pounds light that he was. Adam could only moan lowly, his hand going down to play with his own big dick as he began to worship a man who he once called his equal.
The father watched on the couch, a shit-eating grin plastered to his face as he slowly stroked at a cock that dwarfed Xavier's in every way. The huge, hairy, muscle-laden beast of a father leaned back and let out a low, drawn-out coo as Xavier lifted Adam up almost effortless. He jerked at himself, sending blobs of pre-seed in all directions, as his two eldest sons explored each others mouths with their tongues as Xavier's huge cockhead nestled its way into Adam's asscrack. As Xavier began to air-fuck Adam, the smaller brother lustfully baying with each thrust, the father couldn't take it any more.
The two boys didn't even notice their dad as their pace quickened, each one too into the fucking to see their dad bring the flask once more to his bearded face. The dad drank deeply, his other hand a blur on his massive cock, the roughly hewn hand barely able to even circle around half of his fat dick. All he could think about was the muscle, the cock, the hair. He was the biggest man on the planet, a god among men, and he deserved. Even. MORE.
The dad grunted as his muscles began to overwhelm the span of the couch. What was once meant for three people, it now could barely fit one giant musclebound freak. The giant father grinned as he felt every limb lengthen, relishing as his ribs popped, his spine growing, his shoulders broadening, every bone in his fingers cracking as they all grew longer. It all just meant there would be more room for muscle to pile on! And it did.
The muscled giant huffed lowly as his head was pushed up by his gargantuan, hairy pecs, his dense beard filling in the canyon on the upper shelf of his massive pectoral overhand. His traps swallowed his ears, his deltoids looking like boulders. His arms bloated with freakish power, his biceps and triceps engorging with the magic of the flask, dense, rock-hard muscle pulsing into his frame. His furry abs pushed out of his stomach, so thick, fingers could be lost in the grooves of them.
The big beast of a man had to lean over to see over his giant pec shelf. He grinned as he watched Xavier cum into his other son, Adam. His own megalith of a cock made a low thud as it slapped into the space between his pecs. A devious thought entered his head. He was already so close to cumming, he had to be careful as he gingerly stroked his cock.
"Oh boys," the dad boomed. The two sons looked up for the first time from their fucking to see what their father had become. Their jaws grew slack as they gazed at the sheer size their dad had become. Even standing, the two of them could barely make out his heavily bearded face above pecs that each of them could sit on. The huge monster of a man took the flask and stuck the neck of the bottle into his cum-slit. He roared with delight as cold fluid dribbled its way down his massive length.
"Oh, you boys better get ready..." the dad roared as he dropped the now empty flask and furiously beat off. He pointed his elixer-loaded cock at...