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Tim slung the bags out the back of his old Mustang, and wiped the sweat off his brow. He was home, sort of. Step home, he liked to call it, but still where he’d spent the last four years before college.

And those were pretty formative years – high school, late night drinking with friends, crazy times with girls. He was 19 now, but since his mom died and his real dad remarried, he’d been living here.

He looked up at the large, white suburban front. It was a pretty sweet pad; his dad had been rich, and when he cheated on Tim’s stepmom for some huge-titted model, a lot of the divorce money had gone to Tim and his stepfamily.

As the sun beat down on his face, he realised he was looking forward to seeing them. His stepsister Carly and his stepmom Amber were the closest he had to family. Since Amber’s first husband – Carly’s real dad – had walked out on her (supposedly also for some huge-breasted bimbo), there was a kinship between them.

Tim always wondered if they had a complex about breasts – both had had two major father figures leave for a pair of huge tits on legs, and Tim reckoned that was enough to screw anyone up.

That thought echoing round his brain, Tim grabbed his bags, and strode into the house.

It was smaller than he remembered it. Everything seemed smaller when you went away for a while, and Tim had been away for a whole year, on a football scholarship. It’d been an incredible time; he’d met some great friends, and made it with some amazing girls, but it’d been an intense year, and he was looking forward to taking it easy.

Walking through into the living room only confirmed Tim’s thoughts. It seemed tiny compared to how he remembered it – the walls much closer, the TV smaller, the-

“So, the star quarterback returns.”

A voice came from the doorway to the kitchen. Tim turned around, and a lump formed in his throat, and one threatened to form in his pants. Not everything was as small as he remembered it.

It was Carly. She was standing in the doorway to the kitchen, leaning against it with one arm, the other hanging casually by her side.

Everything about her was the same; she was tall for her seventeen years, with long, tanned legs, which tapered up to denim hot pants, a tiny waist, a beautiful slim face framed by light brown hair and understated make up. All this was the same, except…except…

Tim found himself, for the first time in over a year, lost for words.

Carly had always been flat chested. There was no other word for it. Both she and her mum were tall, athletic types, beautiful in their own right, but never people anyone would describe as busty.

And yet, the figure filling the doorway sported one of the largest pairs of breasts Tim had ever seen. They were stupendous. Large, full, round orbs of flesh, crammed into a tight white t-shirt, cupped by a red bikini which curves against the bulges beneath the packed shirt. They must have been at least an H-cup, but Tim couldn’t begin to process that.

He swallowed again, and felt his cock tingle in his pants. This wasn’t right. She was his sister. Well, his stepsister – it wasn’t like they were related or anything – but they were like brother and sister. Though he’d always found her pretty, he’d never felt anything like this before. She looked incredible – a large busted porn star, filling the door frame with her bountiful chest, curving out like two large melons were tucked under her shirt.

Tim watched her breathe, her massive tits rising up and down as she inhaled and exhaled.

After a period of time, he heard a cough.

“Uh, Tim? Up here?”

He realised he’d been staring as his stepsister’s massive jugs, and snapped himself out of it.

“Carly! How are you? Sorry, it’s been a long journey.”

She smiled a huge, wide grin, jumped in the air (sending her huge melons bouncing madly) and ran to him, jumping into his strong arms, wrapping her legs around his waist, hugging him close to her, kissing him on the cheek.

“I’m so glad you’re back, bro. I’ve really missed you.”

Tim felt really glad Carly’s gorgeous body was a little above groin height, as he could feel an erection building. This was made much worse by the fact that Carly’s huge new tits were pressed into his face. He could feel them, large and warm, as they smothered his face. They seemed…real. How could this be?

Carly hopped down to her feet, her breasts slowly jiggling to a halt, and smiled a grin that no longer seemed just friendly – now it had a sensual edge to it. It sent Tim’s heart pounding. He was starting to realise that he’d never felt this aroused before. Seeing his stepsister with huge jugs was driving him mad with arousal.

Carly turned her back to him, revealing a pert ass packed into her denim hot pants, and looked over her shoulder.

“Let’s go for a swim, big bro. You look hot.” She clacked her teeth together at the end of ‘hot’, in a way that both aroused and confused Tim. Carly had never shown any interest in him beyond the fact that they were siblings. Who was this pumped up sex goddess in front of him? He realised he was increasingly desperate to find out.

As Carly walked out of the room, her huge tits bouncing gently with each step, Tim realised that from behind he could see them emerging either side of her body, like two large water balloons. He was stunned as their sheer width. Trying to think unsexy thoughts, he let his bags fall to the floor and walked dumbly after his stepsister. Or whoever this imposter was.

As he stepped out into the bright sunshine to their marble tiled poolside, Carly was already removing her shirt. She was struggling to pull the base of it up over the two large melon-sized protrusions that rested fatly on her chest. The top half of the shirt was over her head, so she couldn’t see anything, her arms stuck directly up in the air.

“Little help?” Came the muffled voice from beneath the tight t-shirt.

Tim found himself stepping forward, very close to his step-sister, and reaching his arms around her, lifting the shirt up, trying not to touch her huge, wobbling breasts – or even look at them. Once it was removed, he plopped it on the sunlounger, and Carly turned to face him, her face a sultry mask of arousal.

“What do you think?” She asked, tilting her head to the side, and looking down the top of her eyes at him, in a manner that drove Tim wild. She was flirting with him like crazy – what was this?!

Tim tried not to look, but her tits were just too large for him to ignore. She was wearing a large red bikini, but it struggled to cover the breadth of her massive mammaries. It was impossible, but they seemed even bigger than they were in the living room, packed into the red triangles that were supposed to cover her huge chest, but seemed woefully ill-equipped for the job.

“They’re…what did you do?” Was all Tim could ask.

Carly’s gaze flicked to Tim’s large arms, and she closed her eyes, shuddering, placing her lower lip between her teeth. While she did this, she took a deep breath, and her breasts appeared to swell, growing larger, pulsing and throbbing, spreading into the tight bikini even further, her copious tit flesh spreading slowly around the red fabric, like soft dough.

“What do you mean?” Carly asked, coquettishly, opening her eyes as her tits appeared to bulge bigger and bigger in front of Tim’s widening eyes. Her already large cleavage grew even more expansive as her tits slowly pressed together more and more, as they swelled larger and wider, packing more tightly into the limited space presented by the bikini.

Tim could have sworn he was starting to drool. All he could think about was his stepsister’s apparently growing bust. Suddenly, he felt reality calling to him, and he snapped back to it.

“Ok, what the hell is going on, and what have you done with my little sister?”

Carly smiled widely, reaching out with one hand and walking her fingers up Tim’s tight, athletic stomach.

“It’s stepsister, and I’m right here. I’m just not as…little as you remember.”

Tim gulped, feeling a bulge rise in his pants again.

“How?”

Carly bent down, her huge melons squishing down into her knees with the lack of space, and picked up a bottle of tanning oil.

“I’ll tell you. Once you do my back.”

Placing the bottle in Tim’s hand, and staring at him with her gorgeous, brown, come-hither eyes, Carly twirled away, removed her bikini top with a flick of her fingers, and sashayed away to the sun lounger on the other side of the pool.

Tim stared, open-mouthed as the back curve of her huge, wide breasts bounced either side of her slim stomach as she strode confidently to the lounger. He didn’t know what to make of any of this, but his cock was beginning to take over. After a very brief battle he shrugged, and squeezed some oil into his hand.

Carly lay on her front, her arms folded under her head, which poked out to the side. Her breasts looked positively colossal squeezed under her body, and bulged out either side in two large mounds. There was just too much of them. Seeing their size demonstrated in such a stark way was the final straw for Tim; his big cock grew hard in his pants, pitching a full-on tent.

Carly had her eyes closed, so Tim thought he might have gotten away with it.

“Legs first.”

Tim’s mouth felt dry. His heart was pounding.

“You said do your back.” He replied.

“Yeah, backs of my legs. You don’t want me to burn do you, babe?”

“Don’t call me that, please. And this is tanning lotion!”

Carly opened her eyes for a second, and her gaze went straight to Tim’s bulging crotch.

“Oh my god, yes.” She licked her lips, and she appeared to lift her head slight upward, like she was arching her back.

“What are you- stop looking!” Tim blushed red. “You’re my sister!”

“Stepsister.” Carly responded, breathily, rising higher on the lounger. “We’re not related. Which is lucky.”

Tim knew he shouldn’t rise to the bait, but looking at that gorgeous body and those huge, bulging breasts, which seemed even bigger to his mind than before, he responded: “W-why?”

“Oh Timmy. Do try not to poke with that big old pole of yours when you do my legs.”

Tim blushed further. But he had no response. She was driving him wild, and he was beginning to think about doing very explicit things to his stepsister.

He plopped more oil into his hands, placed them together, and knelt down by Carly’s side, rubbing oil into her toned, tight legs.

“Mmmmmm, that feels amazing. Thanks bro.”

“Please don’t call me that.”

“What would you rather I called you? The Elephant Man?”

“What– no! Just call me Tim.”

Tim looked over to Carly’s head, and saw that it was even higher up that before. Was she arching her back, or –

“Oh my god. Are you…bigger?”

Carly indeed seemed to be…growing. Her already huge chest seemed to be rising with each breath, pumping up and up as she lay there.

“You got me, Tim. I can’t hold back any more. Now it’s time to show you everything.”

“Carly, no!”

It was too late. Tim couldn’t turn away.

Carly flipped her svelte body over, revealing much bigger breasts than before. They were like two large, swollen watermelons hanging from her chest, but riding high and pert, with large nipples and wide areolas. They were just colossal, almost as big as her head. Tim’s erection intensified as the blood rushed to his already rock-hard penis.

“I knew you’d like them, Tim. God I love you looking at them like that. You like big girls, don’t you? All men want big breasted sluts to fuck them, don’t they? Don’t say a word. I know it’s true.”

Tim couldn’t speak. Carly was the sexiest thing he had ever seen. He thought he was going to come there and then.

“I never told you how I did it.” Carly continued, pressing her humongous breasts together with her hands, creating a river of cleavage down the middle, as the two watermelons bulged together, causing Tim’s heart to pound even faster.

“There was an experimental hormone they were testing out at the university.” Carly continued, reaching forward to her massive nipples, tweaking them, making them stick out, long, hard and aroused. Tim’s cock did the same.

“I started taking it, and my breasts grew and grew. Oh, it felt so good, Tim!” She was rubbing her nipples harder now, and breathing quickly in and out. “To feel yourself blow up, day after day, swell bigger and bigger and bigger…oh! But-” She was panting now. “There were side-effects, Tim.”

Tim found himself trembling a little. He was scared how aroused he was, and what he wanted to do to his step-sister.

“What…side effects?”

Carly’s nipples were a good inch in size now, and, incredibly, her breasts appeared to still be growing larger.

“Uhhhhh. My libido is sky high, for one. Also…whenever I get aroused, they…get bigger.”

Tim’s blood ran cold. This was too much. If what Carly was saying was true – oh shit, he could see her blowing up, in front of his very eyes.

“I can’t think straight, I’m so horny. If you don’t fuck me I don’t know what I’ll do…mffff.”

Carly was writhing in her seat, her bust expanding slowly forwards, bulging down over her chest as her tits slowly grew bigger.

“Oil me…now.”

Something in Tim’s mind snapped at that point. He knew what he was doing was potentially wrong, but it wasn’t like they were related. Not really. And his libido had almost full control.

He covered his hands in oil, and sat quickly opposite his bulging step-sister, and reached trembling arms towards her enormous, bulbous udders.

His hand making contact was like an electric current between them. Both of them moaned out loud – Carly with arousal, Tim with gratification. They were so large and firm! He squeezed her perfect tits with his large hands, which couldn’t fit around either one in their entirety (a fact which got Tim even more turned on) and began to rub the oil into their huge, pert mass.

Carly began to moan as Tim massaged her massive breasts, and leant back on shaking arms, closing her eyes and biting her lip.

“Oh my goooood, that feels so good!”

Tim began to rub more energetically, kneading the enormous boobs like they were made of dough, loving the response he was getting from Carly, and suddenly noticing them slowly begin to firm up even more, spreading further into his hands. They were growing again!

He loved the sensation of these already huge breasts getting bigger at his touch, slowly swelling up, growing larger and larger as he rubbed oil into their massive bulk, which was growing all the more massive with each successive rub.

“Oh my god, your cock looks so big, Tim. I want it between my girls, right now.”

Tim was beyond protesting. He was surprised he hadn’t come yet. This was far and away the more turned on he’d ever been.

He let go of Carly’s stupendous jugs for a second, and she sat herself upright on the lounger, adjusting her enormous tits, feeling their weight and smiling to herself as they slowly spread forwards, over her hands, bulging larger and larger as she stared at them.

Tim ripped his pants off, and removed his underwear, producing an immensely swollen, rock-hard dick, throbbing, veined and raring to go.

Carly looked at it, and licked her lips, devilishly.

“Mmmm, you’re so big, Tim. Just like me.”

She laughed, and hefted her titanic chest, closing her eyes and breathing in deeply at the sheer lust of it all. Her tits slowly puffed outwards, still growing. Slowly, her arms shaking from the weight of her chest, as well as the deep arousal she was going through, Carly lowered herself down on the lounger, until she was lying on her back, her perfect, humongous tits piled on her chest, sticking up in the sky like two small beachballs, pumped full of air.

“Put your dick between them, Tim. I want you to fuck my tits.”

Tim didn’t even need telling once. He straddled Carly’s gorgeously slim waist, placing his knees either side of her stomach, and moved his big dick closer to the two enormous mounds that wobbled on top of his step-sister’s chest.

The beachballs on Carly’s chest were still slowly inflating, and as Tim moved his cock closer to them, he could see them swell bigger as Carly anticipated the thrill that was to come.

Slowly, agonisingly, Tim slid his cock between the two overstuffed mammaries on his step-sister’s chest.

It felt beyond incredible. The tits were both so packed with fat, that there was almost no give. If you’d poked them, your finger would barely have made a dent; they were stuffed to the brim. This gave them a unique grip on Tim’s huge cock, which slid between them with ease due to the oil.

As soon as his cock was between them, Carly grabbed either side of her tremendous mammaries, and pushed them together, gripping Tim’s cock hard. Straight away, he started to fuck her tits, first slowly, and then building up speed, as her enormous tits acted like a cunt, but so much better.

Tim felt his cock harden with each thrust, as the beautiful breasts gripped either side of it. He wasn’t sure life would ever be this good again. Carly moaned, and he saw one of her hands slide down to her cunt. She was enjoying this just as much as he was.

Tim grabbed both tits, and suddenly, he felt them begin to grow. Carly was so aroused by the whole process, that her tits were getting even bigger.

Tim wasn’t sure if he was going to be able to cope with this. This was too much.

As he tit-fucked his step-sister’s impossibly large jugs, he felt them expand and grow, pressing even harder into his cock, beginning to dwarf it between their enormous bulk. As they swelled and bulged, he saw his cock disappear into the mass of cleavage which was rising from Carly’s chest, and showed no signs of stopping.

Tim’s cock grew harder and harder, as Carly’s tits grew bigger and bigger. They were so huge, Tim could barely see his step-sister’s face, but he could hear her moaning as she fingered herself while he continued to ram her perfect tits.

This was too good to last for much longer. Tim could feel his massive cock preparing to blow its load like never before.

“Oh god Carly, I’m gonna cum!”

“Me too, me too!”

Both of their moans became more intense as their orgasms approached. Carly’s breasts approached the size of stuffed, over-inflated beachballs, dwarfing her head, which they were both almost twice as big as. Tim’s cock was nowhere to be seen. But it felt so good sliding back and forth between them; they gripped it so firmly and beautifully.

And then with one final, apocalyptic roar, Carly’s tits completely absorbed Tim’s cock and electricity shot through him, an enormous stream of cum pumping out of his pulsing dick, shooting into Carly’s waiting face. His dick pumped again, and again, and again, blowing huge amounts of semen into Carly’s face, hair and mouth.

She could barely talk with all the jizz being flung her way, but Carly was in ecstasies of her own, having been brought to an incredible climax by her fingers, and the feeling of her massive, pendulous breasts and her stepbrother’s dick between them.

Tim fell back, sitting on his ass on the lounger, an utterly drained cock between his legs. In front of him, was a parody of a porn star, as his stepsister’s preposterous, over-inflated beachball-sized tits lay bulging up and down on her chest as she breathed, obscuring her face completely. Even now, completely spent, Tim felt a twinge of arousal at how huge Carly was.

He saw the massive breasts rise and fall, and could hear the warmth in the voice on the other side of them.

“That was…amazing.”

Tim rubbed the back of his head with a shaking hand.

“It was. It really was.”

Carly was struggling to get up, but her tits were too large and heavy. She lay back down, and breathed as deeply as she could.

Tim lifted Carly by her tiny-seeming arms, (when placed next to her tremendous tits) and got her up to a sitting position.

“Thanks.” She smiled. She really did look beautiful. Tim thought about it: stepsister wasn’t that bad, really. No matter how close they were. If anything, they were closer now.

“So…what now?” He asked tentatively, holding Carly’s hand.

Still panting, she responded with a devilish smile.

“Oh, just you wait ’til Mom gets home.” She grinned.

Tim felt the blood already start returning to his cock.

This was going to be one hell of a summer.

—

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