The summer house was quiet except for the distant hum of the lake and the occasional creak of old floorboards. Their parents had left for Europe three days ago, handing the keys and the “responsibility” speech to twenty-two-year-old Ethan. At 6’1”, he was the obvious choice to keep an eye on his nineteen-year-old stepsister, Sarah. She was barely 4’10” in her bare feet, a tiny firecracker with a wicked smile and a body that had started turning heads the moment she hit puberty. Ethan had always been protective—maybe a little too protective. Sarah was done being babied.
She’d found the SizeExchanger online two weeks earlier: a sleek black wristband disguised as a smartwatch, sold on some shady fetish forum with a single warning—*irreversible once activated*. Two grand and overnight shipping later, it arrived in a plain box while Ethan was at the gym. Sarah read the instructions once, twice, then practiced the gesture in front of her mirror until her hands stopped shaking with excitement.
On the fourth night, she waited until Ethan was asleep on the couch in front of the TV, long legs sprawled, one arm dangling. She crept downstairs in nothing but an oversized sleep shirt, heart hammering. The device glowed softly as she synced it to both of them. She typed in the numbers she’d fantasized about for months: transfer two full feet. From him to her. Permanent.
A soft chime. A ripple of warmth. Ethan stirred, mumbled something, then settled again. Sarah felt it immediately—like champagne fizzing through her bones. She grew so fast her shirt rode up her thighs, then her hips, then her waist. The hem that once brushed mid-thigh now barely covered the swell of her ass. Her breasts pushed forward, heavy and round, stretching the thin fabric until the neckline plunged between them. By the time the glow faded she had to duck under the ceiling fan.
Ethan looked… small. Pathetic, almost. Still 6’1” in his dreams, but now he was only 4’1” on the couch, his broad shoulders now narrow, his once-powerful arms slender. His boxers hung loose on narrow hips. Sarah’s lips curved into a slow, hungry smile.
She didn’t wake him right away. Instead she went upstairs, raided her closet, and changed. The fuzzy gray cardigan she’d bought on a whim—soft, open, and way too big for her old height—now hugged her like it had been tailored for a goddess. Beneath it she wore the tight white knit bralette that barely contained her new, impossibly full tits. The matching gray terry shorts clung to the dramatic flare of her hips and the long, powerful thighs that could crush a man between them. She left the drawstring untied so the waistband sat low, teasing the smooth skin just above her pussy.
When she came back down, Ethan was just starting to wake, rubbing his eyes. He blinked up at the giantess standing over him and froze.
“Sarah…?” His voice cracked, higher than usual.
She bent at the waist, hands on her knees, letting the cardigan fall open so her massive cleavage hung like twin moons right in front of his face. The scent of her skin—warm vanilla and something darker—washed over him.
“Hey, big stepbrother,” she purred, voice low and velvet. “Or should I say… little stepbrother now.”
Ethan tried to scramble back, but she simply planted one bare foot on the couch beside him, the soft sole bigger than his entire torso. The heat radiating from her leg made his cock twitch traitorously inside his suddenly enormous boxers.
“You’re in charge this summer, right?” She laughed, a rich, throaty sound. “Well, I just changed the chain of command. You’re going to serve me. And you’re going to love it.”
She didn’t give him time to argue. One huge hand scooped him up under the arms like a doll. Ethan yelped as his feet left the floor, dangling helplessly while she carried him upstairs to her bedroom. She dropped him onto the center of her bed—now a vast plain of white sheets—and stood at the foot of it, hands on her hips.
He hesitated. She arched one perfect eyebrow and slowly peeled the cardigan open, letting it slide down her arms and pool on the floor. The white bralette strained; the soft terry shorts rode up the underside of her ass. She hooked her thumbs in the waistband and pushed them down inch by inch, revealing the smooth, shaved mound of her pussy, already glistening.
Ethan’s hands shook as he shoved his boxers off. His cock—still proportionally large for his new size but ridiculously small compared to her—sprang free, rock-hard and leaking. Sarah licked her lips.
She climbed onto the bed on all fours, the mattress dipping dramatically under her weight. Ethan was forced to grab the sheets to keep from rolling toward her. She crawled over him until her breasts hung like warm, heavy pendulums above his chest, nipples stiff and dark against the white fabric.
“First order of service,” she whispered, lowering herself until one thick nipple brushed his lips. “Suck.”
He opened his mouth and latched on. The taste of her skin, the sheer size of the breast filling his face—it was overwhelming. Sarah moaned, deep and satisfied, and reached down to wrap her fingers around his entire cock and balls in one hand. She stroked slowly, possessively, while he nursed.
After a few minutes she pulled back, strings of saliva connecting her nipple to his mouth. “On your back. Arms out.”
Ethan obeyed instantly. Sarah swung one long leg over him and settled her dripping pussy directly over his face. The heat and scent were intoxicating. She didn’t lower herself gently—she dropped, smothering him beneath soft, swollen lips and the slick heat of her folds.
“Lick, little stepbrother. Make your giant stepsister cum.”
He licked like a man possessed, tongue working her clit, sliding inside her, tasting every drop. Sarah ground down, riding his face with slow, powerful rolls of her hips. Her huge thighs framed his head; her ass smothered his chest. When she came the first time, her juices flooded his mouth and chin, and she let out a long, shuddering groan that vibrated through both of them.
She didn’t stop. She simply lifted off, turned around, and lowered herself again—this time facing his cock. Her mouth—hot, wet, and huge—engulfed him completely. One slow suck and his hips jerked helplessly. She could fit his entire length and still swirl her tongue around his balls. While she sucked him, she reached back and spread her ass cheeks, pressing her still-wet pussy against his face again.
They stayed like that for what felt like hours—69ing with her completely in control, using his body as her personal toy. When she finally pulled off his cock with a wet pop, strings of spit and precum connected her lips to his throbbing shaft.
“Time to fuck your owner,” she said, voice husky.
She spun around, straddled his hips, and guided his cock to her entrance. Even though he was smaller now, the angle and her arousal made the stretch delicious. Sarah sank down in one smooth motion, taking every inch until her clit ground against his pelvis. She was so tall that when she sat upright, her head nearly brushed the ceiling fan again. Ethan stared up at the towering goddess riding him—breasts bouncing, cardigan long forgotten, nipples hard, lips parted in ecstasy.
She rode him hard. The bed creaked dangerously. Each downward thrust slammed her weight into him, pinning him to the mattress. Her pussy clenched and fluttered around his cock, milking him.
“You’re going to cum inside me when I say,” she panted. “And then you’re going to clean every drop out with that eager little tongue.”
Ethan groaned against her thigh, nodding frantically. Sarah smiled down at him, eyes half-lidded with lust and power.
“That’s my good little servant.”
She slammed down one final time, grinding her clit against him as her second orgasm ripped through her. Her walls pulsed so hard he couldn’t hold back. He came with a strangled cry, pumping rope after rope deep inside his giant stepsister while she kept riding through both their orgasms.
When she finally lifted off, a thick trickle of their mixed cum leaked from her puffy folds and onto his stomach. Sarah looked down at the mess, then at his exhausted, blissed-out face.
She leaned down, breasts dragging across his chest, and kissed his forehead almost tenderly.
“Summer’s just getting started, tiny,” she whispered. “And I’ve got a whole list of ways I want to be served.”
She straightened up, still straddling him, and ran her fingers through her hair, looking every inch the 6’10” goddess who now owned her 4’1” stepbrother completely.
“Round two in the shower. You’re washing every inch of me. With your tongue.”
Ethan’s spent cock twitched again at the command.
He was never going to be in charge again. And he had never been happier.
