A Tale of Two Brothers: Donnie & Marco

by Artotter92   

Two brothers end up the unwilling subjects of their father’s science experiments, with some pretty extreme results.

There was nothing particularly remarkable about brothers Marco and Donnie Diaz. Born to a mixed white and Latinx family they were raised predominantly by their father, Mr Diaz, after their mother walked out when Marco was just 6 and Donnie was 2. Mr Diaz worked for a local private science group and their lives were perfectly normal and respectable—they went to church every Sunday, Donnie studied hard and Marco hardly studied now he’d graduated high school and dropped out of community college after a couple of years.

Out of the two brothers Marco, the older at 20 years old, was definitely the less inclined to hard work and study. He enjoyed gaming, drinking and sleeping in until well past midday—oh, and masturbating, of course. He was handsome, and had broken more than a few girls’ hearts with his tanned skin and thick dark chestnut-brown hair. He favoured sportswear and silver jewellery such as his fine silver chain necklace. If there was one thing he hated though it was his glasses and he swore to get laser eye surgery when older. The one thing Marco did put effort into was sports and he particularly enjoyed basketball, despite being only 5’9’’.

Younger brother Donnie on the other hand was an adorable 18-year-old, but more in the way that you just wanted to take care of him. His skin tone was paler but his thick tousled hair darker and he was even shorter than his brother at just 5’6’’. Like Marco, he too wore glasses, though they complimented his bookish personality. Whereas Marco liked dark clothes, Donnie favoured bright, peppy colours and wore a silver crucifix hung around his neck. Donnie studied hard and clearly had a similar mind to his father, fascinated by science. He was shy though and kept his head down, he did not have his brother’s confidence.

Donnie and Marco didn’t always along and were prone to arguing or fighting, usually provoked by Marco when he was bored or restless. This was worse during the week when their father would leave them to look after themselves now they were both of age. Recently his work had meant he was frequently away until late at night, leaving the boys to look after themselves. Though Marco was in technically in charge, it was unsurprisingly Donnie who took up most of the cooking and cleaning.

“What are you working on, dad? What’s the top secret project?” Donnie would ask excitedly, his scientific brain whirring with possibility. But Mr Diaz would only chuckle and say it was more than his pay grade to tell Donnie that. After Mr Diaz left the room, Marco would snigger and flick balls of paper at Donnie calling him a “nerd”, though he too was privately curious. Over weeks the brother’s curiosity would lead to them trying new methods to getting their dad to share what his work was—Marco believed it must be some sort of secret FBI technology whereas Donnie felt it must be a project for sustainable energy. Mr Diaz however never gave anything away. The brothers didn’t even know the name of the company their dad worked for!

Their routine continued unremarkably until one week where Mr Diaz abruptly announced he would be away the full week for work—it was a crucial time for the project and he needed his sons to look after themselves. That same Monday morning he loaded up his car with his briefcases, laptop, loading cases and other paraphernalia and gave his sons a big hug goodbye.

“You look after your little brother, now—you’re the man of the house after all” he joked, tousling up Marco’s hair, to Marco’s annoyance. Donnie smiled resignedly, knowing it would be a week of Marco doing sweet fuck all, whilst Donnie tried to keep on top of things, all the while that Marco would either be in his room jerking off, off out drinking with mates, or existing purely to wind him up.

They watched their father drive away before Donnie headed back up to his room and study. Marco however wasn’t going to waste a minute. Although Donnie was the one always asking about his father’s work, Marco was dying to find out. He might be lazy, but he wasn’t stupid and his father’s secrecy was more than enough to raise his suspicions. Hell, if it was some Musk level science shit their might be some serious money! So as soon as his dad was out of sight and Donnie was in his room, he snuck into his dad’s study.

The room was called a study but was more like a home laboratory with multiple screens, fridges, freezers, centrifuges and test tubes. And it was a bombsite. Marco stared in shock—it looked like it had been raided, or that Mr Diaz had left in a hurry. Cupboards were open, scraps of paper everywhere, lights flashing. Marco held his breath as he looked across the notes and logs and calculations—only nothing made sense to him (he was not a natural scientist after all).

For a full half hour he carefully searched for some hint of what the project was when he discovered two vials in the smallest fridge, filled with bright green liquid. They were labelled differently:

“H1-M80 formula: premium. Masculinity and Virility certain.”

“H1-M80 formula: unbalanced, Effects uncertain.”

Now, he may not be bright but he knew what masculinity and virility meant. He looked again at the notes strewn around him—phrases jumped out at him, now making more sense: “increased libido,” “significant mesomorphic growth,” “testosterone output exponential.” He also knew that his future didn’t lie in hard work and study. He grinned as he pocketed the two left over vials—he knew what he planned to do with one but it would be a shame to waste the other. He chuckled softly to himself as he looked up to a framed photo of him and his stupid, dorky brother Donnie…

“But you never make dinner?” Donnie said suspiciously as they sat down for Marco’s homemade curry that evening.

“Well bro, I realise I’ve kinda been a dick to you and… well, I just wanted to make it up to you this week. Now—eat up!” said Marco, uncharacteristically sweetly.

The curry in fact didn’t taste half bad! Though there was something about it which tasted… different to any other curry Donnie had ever had before. “Marco, what exactly did you put in this curry?”

“Oh, just some… buffalo sauce. Secret recipe tip,” Marco lied, quickly and efficiently.

“Well, I guess it did the job!” Donnie tossed a wary smile at his brother before tucking into the rest of his meal.

The next morning Donnie woke up feeling like his head was full of fog. As he stretched he didn’t notice that his bones seem to click and pop a little more than usual. He winced as his watch felt like it was digging in, so he loosened the strap. Wearing just his pyjama pants he frowned at his more-persistent-than-usual boner. He chanced it and hesitated before heading into the corridor to head to the family bathroom. He let himself in and gasped suddenly as he saw himself in the mirror, pyjama bottoms tented. Firstly—his previously slightly doughy body was toned now—he had a flat stomach and even a slightly proud pair of pecs. A dusting of dark hair worked up his abs and he gingerly touched the growth of small dark hairs on his top lip.

“Looking butch, bro,” chuckled Marco’s voice and Donnie span round to see his brother—once taller, now a similar height, stood in nothing but bulging boxer shorts. He too looked buffer—he had always been lean but now he looked like an actual gym-jock. Donnie’s eyes couldn’t help but rake over the broad tanned chest and impressive bulge before he yelled and shoved his brother out the room before he washed and hurriedly shaved his face smooth again.

Later, as he was forcing his way into a now too-tight t-shirt ,which now revealed an inch of belly and those pesky trail hairs and showed off his new lean body shape, he noticed with horror that the hair on his upper lip had grown back, thicker and darker than before.

He tried to spend the rest of the day as normal, but he couldn’t help the looks he got in the coffee shop (was the nerdy, twinky barista actually checking him out?) or the librarian asking if he was feeling okay, as he could feel his clothes getting tighter. Donnie just nodded his head, stifling a groan at the pain in his stomach.

As soon as he got home to his room he tore off his clothing and, shocked at his own pent up horn, jerked off over his bed before passing out to sleep as, unbeknownst to him, Marco grinned and watched through the door crack, gently rubbing his own package.

The next afternoon Marco laughed to himself in the mirror as he hauled his naked ass out of bed. His small pecs had increased in size and his arms ache as his forearms looked thicker and meatier. His biceps were swelling a little as his hands too look broader. Marco could feel every bit of pain in his transformation as his spine lengthened his back, making him just a little taller. His feet had grown outward, by a couple inches, as his butt stood pert, round and proud. His cock and balls began to swell and grow more as his balls filled with new fluids of a man growing, his legs feeling heavy as his calves bulged out. Marco didn’t even feel the changes, only the fresh breeze on his exposed new cock and balls, which he fondled shamelessly. Sexy stubble peppered his chin, but unlike Donnie he didn’t seem to have grown any body hair—if anything it was starting to retreat. What was once a thick bush was now stubble around his thick cock. He fingered a drop of pre as he heard his bro yell in shock as he too woke up late and stumbled to the mirror.

Donnie stood before his mirror, hands clutching his body as his pecs bounced and slowly swelled. His arms were even larger than the day before. His legs were getting more muscular, too—years of intense workouts couldn’t even compare to what his legs seem now. His abs had pushed out of his flat stomach, forming a nice 6-pack. His Adam’s apple too had grown and was now quite prominent as his groans got deeper. His facial hair was growing at a faster rate than before, giving him a clear developing moustache as well as stubble across his jaw. His skin felt tight as his acne started to fade away. “What the actual fuck?” he whispered, before gasping at his new, lower voice.

He ran to his brother’s bedroom and stopped in the door as he saw Marco reclined on the bed stroking his thick, uncut cock. “Sup bro,” Marco said with a wink.

Donnie backed out the room, scrambling back to his own closet to pull on some red joggers. He stocked up on food from the kitchen and returned to his room, locking the door, only he couldn’t get the image of his muscled-up bro stroking his cock out of his head. He curled up in bed and slipped into an anxious sleep.

Meanwhile Marco spent the afternoon switching between jerking and sending pics of his new body and cock to all his Snapchat contacts—male, female, he just didn’t care. He wanted to show off! Many didn’t believe him, but it didn’t matter. He just liked the attention of it all.

Donnie woke up that evening to his head having this painful throbbing sensation. He ran into the bathroom to see if there was anything to treat the headache, but there wasn’t. The pain got worse gradually. He clutched his head as his deep groans filled the room. The ache was too much. His tears ran down his face. He wanted it to stop, but it didn’t. In fact, the headache started to feel like it was changing him. He tried to concentrate, but found it difficult to even think of a solution. Usually, whenever he had a problem, he could figure it out in the matter of seconds, but now this was a problem he couldn’t solve. Tears stung his eyes as the pain of his head felt worse, his thoughts all foggy and uncertain, unable to think much.

The one thing stick in his head was that image of his brother on the bed. Slowly, almost unwillingly, he released his thick cock from his red sweatpants and, grabbing one hand around his dick, started stroking. He had never been like this. Each stroke was making him feel better in many ways. Donnie’s jaw dropped, allowing saliva to fall on his dick.

Thoughts of his bro’s body and cock filled his head and he liked it. He imagined his brother’s butt jiggling and cock swinging as he felt pressure build up in his dick. He was going to release. Donnie was ready and didn’t care where it would land, as long as the dumb headache would go. And it did. Donnie let out a white stream of cum as he laughed dumbly, the stream splattering up his abs and his pecs… wait, his pecs!? He scrambled to his feet and the panic returned as he noticed those tight pecs had grown… only now they were round and bounced as he panted… hell, they were almost like breasts.

A cold sweat broke over him as he muttered to himself, “What in the name of heck is happening to us…?”

“We’re becoming Gods, bro,” came a voice from the door, and Donnie looked over to see Marco flexing as he winked once more. “Oh, and thanks for the show!”

The next afternoon Donnie woke up in a big sweaty mess as he grunted and grown—a mix of plain and erotic pleasure. He started grinding on the bed not being able to control himself at all. He tried to stop but it feels so good. His body was producing an odor of a heavy sweat. He could feel his body swelling again. His pecs were bulging and becoming rounder, his arms becoming bigger as more dark hair sprouted over his body. His very genes were rearranging. He didn’t even realize how big he was getting, since he was too busy fucking his bed. His balls were growing larger as Donnie moaned, his nipples spreading and growing wider. He used one hand to rub them as he moaned louder with each thrust put into the bed.

He could feel his head aching again as he needed to release his cum. He needed to breed. He needed to fuck something. Donnie was terrified but at the same time he secretly loved it. His feet had grown larger as they hung off the bed, also sprouting dark hair along the broad upper surface.

He was so big now. Donnie’s appearance changed as his face matured, looking older—more like a man in his 30s now. The pressure was building up, becoming too much to hold back, and the bed sheets were filled with sweat and pre cum. He moaned loudly one last time as thick cum spurted over his round chest, face and headboard. Donnie rolled into the big mess he had made with his mouth open and tongue out, trying to lick up anything he could. Donnie couldn’t control himself anymore. He just needed cum. He didn’t want anything else. All the time he’d wasted studying, when he could have been jerking his cock!

Donnie walked up to his mirror, noticing how big he was and how different he looked. He fucking loved it as he flexed his huge hairy arms. He loved how big and bouncy his balls were. Even if he shaved, the monster of hair on his balls would grow back in the matter of hours. He wiped away the drool on his face as he rubbed his large nipples. He loved the feeling and so he rubbed more vigorously, vaguely wondering where his hot brother was.

Meanwhile Marco was already out. He’d got up early and hard as a rock. His height had shot up overnight, as had his muscle mass and cock size. Pulling on some tightly stretched active wear, he ventured out into the world in search of some release.

He found it when he swaggered into the coffee shop his bro would always go to—and there he was, that nerdy, kinda cute barista who was clearly gay, nametag reading ‘Joel’. As he ordered a latte, he leaned forward and whispered into the nerdy twink’s ear to meet him round the back in 10 minutes.

10 minutes later, Marco’s moaned echoed round the back of the building as Joel gagged and tried to take in his huge cock in his mouth. Between slobbering and sucking the twink would marvel at Marco’s tanned huge muscles, and Marco would just laugh and cock slap the barista. Joel used both his hands to rub the huge dick and inhaled the sweat from Marco’s hot hairless body. He bathed the huge balls with his tongue as pre spurted and stained his apron.

He was so taken up with his task that he barely noticed Marco’s dick getting larger and fatter, or even that the foreskin seemed to fade into his fat, long, dick. Marco’s head hair remained full, though it receded slightly up his forehead as his face matured more—jawline pushing out and lips plumping up. His swollen pecs and abs become more noticeable as they bulged yet bigger.

It wasn’t long before Marco roared and shot thick, gloopy cum over Joel’s face. Joel collapsed spent and stared up at the God.

“Are you free this evening?” the barista panted.

Marco just laughed cruelly and took a long piss just feet away from where Joel lay. “Not for you, nerd,” he scoffed before tucking his bulge back in his sweatpants and walking away.

Joel just lay there in the cum, dazed. Why did he always fall for the big douchey men, why couldn’t he find a nice guy—like that Donnie guy who always came in. Thinking of which, he hadn’t seen Donnie in a few days now…

The two brothers stared at each other in the kitchen. Both had changed so much they’d started to look unrecognisable. Marco’s stubble had pushed out into a goatee as his bodybuilder sized bronzed mahogany body rippled. He once again stood over the younger Donnie, who looked significantly older than his bro now—lines across his face as a moustache bristled over a heavily stubbled chin. They were both stark naked, both cocks well over a foot long.

In a brief moment when the fog had lifted, Donnie had understood. He stared at Marco with sadness and fear as he whispered, “What did you do to us?” He then gasped and clutched his round pecs as they inflated and grew bigger than his head, his bubble butt swelling out real thick as specks of grey appeared in his dark hair. Thick dark body hair not only covers his pecs, surrounding wide saucer sized nipples, but also his ass, shoulders and lower back. His abs pushed out, softened by the layer of paunch on top.

Marco too felt his mind fading as his massive square pecs pushed out, obscuring his view of his feet. His lips swelled as his eyebrows got thicker and more unkept. His face aged up too, grey streaks appearing through his thick dark chestnut hair. His brown nipples swelled wide, though his chest and nips hardly compared to Donnie’s tits. He played with his smooth pecs and huge nipples as his once-younger little bro stepped closer, breathing heavily.

Marco moaned as he felt Donnie’s hand encircle his heavy cock. He nodded in encouragement, maintaining intense eye contact with Donnie. Donnie lowered his eyes and started to suck on Marco’s big brown dark nipples. His veins swelled and flexed as the taller man’s muscles expand even more, his height creeping up. His feet swelled disproportionately large for his body, as did his hands, giving him an almost primal look. His cock spurted pre violently as it swelled like a balloon, his balls hanging lower.

Donnie bit his lip and seductively turned round, bending over and revealing that what was once a tight pucker is now a throbbing, swollen donut ring of a hole between two hairy globes.

Marco licks his lips…

Some weeks later

NastyPig was one of the most famous leather and kink clubs in the USA. Men of all sizes and tastes gathered from across the states to descend into debauchery, and tonight was a special night.

On the raised stage was a banner with bright red letters encircled on a black background: “D&M”. Onto the wiped-clean stage strode two Gods of men. One, aged maybe mid 40s, was a 7 foot, ultra-tanned, goateed muscle god. His shoulders so wide revealing a barrel chest with two brown nipples the size of dinner plates. A thick cock, at least two feet long, swung below his meaty thighs.

The other man was mid-late 50s and was shorted but wider. He had a kind friendly face with a salt and pepper moustache. But the most remarkable thing about him were his colossal bouncing tits, with enormous nipples the size of dinner trays. A silver crucifix on him looked absurd on clearly such a pig of a man. Both men wore leather harnesses, and also glasses. It was an unorthodox choice for two such virile, masculine men, but their fans felt it gave them a unique look—like nerds gone butch.

The two men on stage faced each other and started sensually making out, the taller one reaching round and unmistakably slipping a thick finger inside the other’s puffy hole.

One musclebear leaned to the man next to him and whispered: “Y’know, I heard they’re secretly brothers?”

Mr Diaz smirked and nodded as he watched the show escalate until the shorter man with the breast-like pecs was on all fours, panting and moaning like a slut as the taller muscle man pushed his whole hand in his ass, right up to his elbow.

“I know.”

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