Timmy sat up, his hands digging into Jamie's coarse-haired chest. The bigger brother winced at the feeling of his blond younger brother's nails digging into his skin, but it was a fraction of the pain that Timmy was feeling. The younger brother's hands trembled as he felt every joint in his body build more bone. He huffed as his limbs lengthened, the stretching of his muscle and skin audible as they tried to keep up with the growth of the blond titan's bones.
Jamie tried in vain to get Timmy's attention, waving his hand in front of his brother's face, shaking Timmy's shoulder, to no avail. Timmy's eyes instead rolled back in their sockets, his mouth agape as he was lost between the realms of pain and pleasure. Jamie watched in twisted fascination as he saw the bones in his brother's face reconfigure; his brows getting more prominent, his cheekbones more defined, his jaw thickening even further. Jamie shook his head as he watched the visage of masculine perfection get further from his own as Timmy continued to grow taller. It took a moment for him to register that this wasn't like the daily growth spurt Timmy had yesterday.
Timmy got off of his brother, stumbling to his feet as he climbed off the bed. A sense of vertigo overtook him as he widened his stance and looked around at his new, taller vantage point. Bewildered, Jamie got to his feet as well. Both brothers were shocked to see Jamie's lust crown of hair only come up to Timmy's collarbone.
The growth had left Timmy looking rather emaciated. His body had built an insane amount of new bone, while the softer tissue had yet to catch up. His previous world-class open-bodybuilder proportions had changed to that of a lanky long-distance runner. But just as Timmy thought his growth spurt was calming down, the intense burning that flooded his joints moved to every muscle fiber on his body. The blond beanpole screamed in agony as the pain redoubled itself.
Jamie, momentarily forgetting that his brother was now a head taller than him, quickly embraced his brother, worriedly shaking Timmy, telling the younger brother to hang on. His worry quickly turned to dread when he heard the words coming out of Timmy's mouth.
"Oh... fuck yeah," the blond giant hissed. Jamie's eyes went wide as he could feel the muscle building underneath Timmy's skin. He looked up to see his younger brother's face screwed in a contorted expression of hedonistic, rapturous pleasure. Unhanding Timmy, he stepped back and yelped as he watched Timmy's body explode with new size and strength.
Everywhere, muscle piled on top of muscle. If Jamie had a build that would make the Hulk turn pale, Timmy was on another level of muscular development. Timmy's neck exploded with corded mass, his traps bunching up with so much mass they threatened to touch his ears. His shoulders, one moment you could see the underlying bone, blew up into rounded, bloated boulders, etched with striations and veins. Tim's arms, once thin and wirey turned into colossal pillars of brawn, his forearms a grotesque bundle of sinew and strength.
Timmy groaned, using his newfound size to pull Jamie close. The shorter, hirsute giant whimpered as his mind was immediately overtaken by his lustful desires, his hands automatically moving to up to cup at the heavy and growing pec shelf on Tim's increasingly titanic chest. His tongue shot out to lap at the salty, ferrous-tasting sweat, the coarse buds of his tongue scraping against the thick dark-blond hair of his brother's chest. Timmy moaned approvingly as Jamie's hands moved down to graze over the expanse of his abdominals. His brother's fingers lingered in place, twirling at the sweat-soaked locks of each set of abs; stopping at the first pair, then the second, third, fourth and finally fifth, a 10-pack in total.
Timmy's arms wrapped around Jamie, using his new strength advantage to easily lift Jamie off the floor so that he could kiss him on the lips. Jamie stole glances of the incredible development of his brother's ass over the swell of his gargantuan traps. The thick muscle bubbled into view as it grew more with each passing second. Jamie's shins brushed against the hairy forest growing on Timmy's thighs, feeling how the muscle pushed his feet in further as the quads developed.
"Oh fuuuuck, Jamie, I feel incredible!" Timmy bellowed, his voice like an earthquake. He switched over to holding Jamie up with one hand as his adjusted his pose so that he could stroke his now comparatively tiny footlong cock. Jamie's eyes roamed over Tim's vast expanse. His brother was beyond huge now, more man than any that came before. The beast of a boy was almost as wide as he was tall, his muscles coursing with fresh energy, enhanced power!
Without words being exchanged, Tim plunged his cock into Jamie's ass, the brothers groaning in unison, Tim's voice a whole octave deeper than Jamie's. The hulking beast pistoned his hips into his brother, Jamie bucking up and down as Timmy used him as little more than a glorified fleshlight. Timmy's huge hand wrapped around Jamie's waist, pushing and pulling him up and down his cock as he used the other to explore his enhanced body further.
As rough as Tim was, it only got worse when Jamie began to feel Timmy's cock begin to grow inside him. It started with his prick penetrating another inch, causing Jamie to bay in delirious pleasure, sending a huge stream of pre-seed that jettisoned into Timmy's thick beard. The bigger man lapped up Jamie's gift and slammed harder as his cock surged even larger. Jamie's head bobbed like a ragdoll as Timmy fucked him harder and harder the bigger his dick became. Soon, Timmy was lifting Jamie over a foot with each thrust, slamming his brother down further to his base. The impact caused balls that grew in pace to slap with a loud 'thwack' into the small of Jamie's back with each thrust.
"Jamie, I'm--" Timmy was cut off short as Jamie's thick cock sprayed seed all over his chest, chin and face. The blond hulk sputtered as guzzled pints of fresh cum. And avaricious vice took over him and he bent over and inhaled the tip of Jamie's cock, causing the smaller, yet older, brother to howl with pent-up need. In moments, he too was flooding Jamie's ass with a tidal wave of cum, pumping gallons of his superior seed into the smaller giant.
Jamie felt his guts begin to push out, the protrusion of Timmy's cock no longer visible through his abs as the space was filled to the brim with the younger brother's potent cum.
Timmy laid his brother back on his bed, smiling at how much he'd just filled Jamie out. He pulled inch after new inch in both length and girth out of Jamie's hole; over two and a half feet of it, the rod as thick as his forearms. With one last spurt, he glazed Jamie's entire body in his sperm.
"Fuck, let's go again!" Timmy exclaimed, looking down at his exhausted brother. He flashed Jamie a big, goofy grin as threw his arms up in a big double biceps flex. Jamie just groaned in response.