Jamie almost let out a whimper as he stared at his 'enhanced' little brother. Little Timmy's body had transformed into the kind of guy he jerked off to in his head -- a hot 20-something with bulging muscles and an even bigger dick. It didn't help that Timmy was busy stroking what must've been one of the largest cocks he'd ever seen beside his own. Jamie moaned as he felt a huge dollop of pre-seed erupt from the tip of his shaft, lewdly splashing onto the tiled floor of the bathroom.
"Look, Jamie," Timmy boomed, a confidence in his voice, it made Jamie almost go weak in the knees. Gods, his little brother even sounded hot... The muscled blond Adonis raised his right arm, bunching the muscles up like a bodybuilder would. Jamie practically drooled at the sight. "I got muscles like you now! And they feel so good," Timmy grunted as he brought his hand down to join the other in pleasuring his big 10" behemoth. The younger brother's eyes roll back as he stroked faster, lewdly moaning with delight. "It feels so good, Jamie. Now I know what you feel like when you do this."
"Timmy, stop!" Jamie pleaded, more for his own sanity than anything. "You can't just pop a boner and jerk off whenever you feel like." He knew it was fruitless, for he was already starting to lose to the urge to pleasure his own monstrous needs.
"Is that what it's called?" Timmy said between punctuated breaths, the stud close to the edge, his eyes half-lidded. He smiled as he looked down at his massive, bobbing shaft. "I like my boner," he cooed. He looked up and gave Jamie a wicked grin. "Wanna see what I can do? I've been jerking off all morning!" Jamie blushed, the thought of his brother rubbing one out all morning was almost too much.
Timmy hunkered over and cupped his massive cock and balls in his hands, guiding the fat cockhead to his mouth. The stud flitted his tongue out and grimaced at the sheer sensitivity of his own shaft, rewarding himself with a juicy dollop of jock-milk. "Mmph, it tastes so good. I really like cum and it feels so good making it," he rumbled as he worked his shaft with his strong hands, his thick, 20" biceps rolling and the veins in them dancing.
"Timmy, no," Jamie growled, the inner beast clawing its way to the surface. His voice grew hoarse, his eyes glued on his smaller brother's delicious assets. He could feel the urge to fuck growing. He wanted to dominate that stud, make him his... But Jamie knew better... he was in control for now. The massive, hirsute behemoth roared, "I said, 'stop!'"
Timmy yelped and instantly took the head of his shaft out of his mouth. At first, Jamie thought Timmy was simply following instructions. But he noticed something was off about his little brother. Timmy started to sweat, his meaty hands beginning to tremble.
"I feel really... warm, Jamie," Timmy moaned. Jamie's eyes went wide open. Oh no... it couldn't be. Unbeknownst to both of the boys, Jamie's 'special' seed had not only accelerated Tim's physical development, but put him on the same daily growth spurts Jamie was going through. And Timmy... well, he was going through the throes of his very first one.
The blond hunk screamed as he felt a pressure develop in his nuts, it felt like they were exploding. And in fact, they may as well be. Jamie's cock lurched as he watched his brother's hen egg-sized nuts swell, growing to the obscene size of small apples. Tim took sharp breaths, feeling the tissue almost bubbling underneath his skin as his rod lengthened, his massive 10" tool growing to an impressive 12", a whole foot of epic cock. His body followed suit.
Tim snarled as he felt his spine popping. Extreme pressure radiated from his elbows and knees as bone and cartilage grew and ossified, the boy beast growing another 2 inches, his body riddled by a pleasurable agony. He could feel his sinuses pop as his face restructured, become even more masculine. Tim let loose a roar, and Jamie couldn't help but begin to stroke himself as he looked at how handsome his brother was becoming. Jamie couldn't resist any longer. He could feel a deep shame well up from within him, but his lust compelled him onto his knees. The brown-haired behemoth lunged forward and took Tim's massive 12" prick into his mouth, the hulking mass of muscle shuddering as his tongue lapped up the salty pre that was coating his stud-brother's cock. He massaged Tim's swollen nuts with his left hand as his right hand roamed up and down his own engorged 19" monster, so thick his hand couldn't even reach around it.
Tim was smiling now, feeling the pressure pushing out from his muscles -- and muscles, well, those were his favourite. The blond musclestud reaches down and plays with his brother's soft brown hair. Here he was, a stud with the body of a bodybuilder getting serviced by his Hulk-sized brother. What could be better? His body had kept his muscular, middleweight bodybuilder's proportions as he grew taller, but that was about to change. As his massive big brother sucked his cock, Tim roared as his felt his favourite muscle begin to expand -- his pecs. He felt the skin stretch taut over the expanding muscle. He instinctively reached up with his free hand to cup at the massive pec shelf that was developing. Drool pooled at the corner of his mouth as he struggled to reach up, his biceps growing to a massive 24", fighting for space with his growing chest and lats. The growing musclebeast moaned lewdly as he rolled his shoulders, adding so much width he wouldn't be able to go through a doorway without turning to the side ever again. Tim began to buck his hips, his powerful thighs fighting for more space and the growing hulk adjusted his stance. Jamie whimpered as he felt up Tim's thick thighs, his hands roaming back to Tim's steel-like glutes.
Jamie looked up, unable to see his brother's handsome face beyond his shredded abs and epic chest, but he could hear Tim's breath beginning to get laboured. "Jamie... I'm gonna... cum," Timmy wailed. Both brothers moaned as they blew their loads. Jamie's burst out behind Timmy, coating the entirety of the bathroom in his teen-god spunk. Tim thrust forward, the heavyweight bodybuilder flooding his hungry musclegod of a brother's mouth with his nutritious mancream. They both ride out their orgasms, each lasting what felt like minutes.
As Jamie pulled out, he stood up and admired the man his brother had become. With an exhausted smile, Timmy brings up both his 24" arms, veins dancing along the surface, his body looking like it belonged on stage, defeating any Mr. Olympia. He stood at an impressive 6'4" and his 12" cock bobbed with need, just finished but ready for more...
And Jamie... despite his better nature... was ready too...