Thread by @murcielagoAO3

#miyacest fraternal twins, fem!atsumu, puberty things

They're not that different in personality or behavior or even looks until puberty hits and Osamu shoots up four inches in a single summer and Atsumu suffers the unique humiliation of going bra shopping for the first time.

Osamu teases her relentlessly the day they notice her chest has started to change. Unlike flat-chested, scrawny eleven year old Osamu, the tiny mounds under Atsumu's puffy nipples turn the horizontal stripes of her tank top into wavy lines, marking her as /not a boy./

Osamu points and snickers. "Looks like ya stuffed coupl'a grapes in yer shirt!"

Atsumu's mouth falls open, and all she can manage is to turn red and yell at him to "SHUT UP!" through gritted teeth. She can kick him too, she realizes, and she tries, but he blocks and skips away.

His laugh is insufferable. "Oh 'scuse me, my mistake—meant /raisins/ 'stead of grapes!"

Atsumu splutters, red all over from shock and horror. Then he does the unthinkable—he /pinches/ her nipples in both hands before she can realize his aim.

"Honk-honk!" he brays in her face.

Atsumu shrieks and crosses arms over her chest while he skips out of her range, but then he hovers nearby, hopping foot to foot like he's going to dart in again any moment. Her nipples /hurt/ and her eyes flood with fat tears, mortified beyond comprehension. Then she's /furious./

"Stay away from me!" she roars, charging Osamu at full speed, teeth bared and eyes a little wild. They're not different in size yet, nor speed nor agility—fueled by rage she overtakes him on the opposite side of the school playground right by the street and tackles him

to the ground, pommeling him with fast snaps of her fist until his lip and his nose are bleeding everywhere and some teachers pull them apart. She wriggles out of their grasp and runs all the way home by herself—or that's her intention when she remembers she doesn't have a key.

She turns around and goes to the bench along the bike path behind the school, thinking she'll just wait until school's out and their dad is home. But that makes her cry again, because she doesn't want to see him either, she just wants to go lie down in her bed and sob forever.

She sits with her knees under her chin, hugging her shins for what feels like an eternity before she notices people coming towards her from the direction of the school. It's not just her teacher and her brother—it's her dad too. Atsumu's heart seizes in her chest, and she bites

her lip against the urge to run away as fast as she can go because if her father's there, it's useless and she knows better.

She watches them come with hot tears trailing down her cheeks. She sets her mouth in a stubborn line and hugs her legs tighter.

Osamu's got a bandaid

on his lip and gauze stuffed up his nose. One of his eyes is starting to purple and she takes some satisfaction from that, though it's pretty clear she's the one in big trouble for losing her temper and running off without permission.

Osamu approaches her first. "Sorry, Tsumu."

She narrows her gaze at him. The words sound like he was told he had to apologize but he doesn't really mean it, and she feels a flash of anger through her ribs.

He must tell that she's not buying it, for he clucks his tongue and comes over closer, dragging his feet and sighing.

He squats down in front of her and looks up through his bangs. "I said, /sorry,"/ he insists. "Took it too far. Shouldn'ta teased ya like that."

She presses her lips into a frown. "Yer mean, 'Samu, an' I hate ya."

He flinches at this, then scowls and bucks up. "Well ya nearly

broke my nose! Ain't we even, then?"

Atsumu bristles, setting her shoulders. "Ya deserved whatcha got! An' /then/ some!"

Osamu sucks in a breath like he's preparing to let loose a slew of insults at the top of his lungs, and that's when their father steps in to diffuse things.

"Now listen, kids," he says, holding a hand up to each of them. "It's important to talk things through and find a way to get along with each other. But for now, why don't we just head home okay?"

Atsumu looks between her father and brother. She's not opposed to going home, but

she doesn't see why her brother has to go too. Osamu stands up, crossing his arms and sighing. Everyone looks at her, expectantly.

"Ready to go?" her father says, now holding a hand out for hers.

A frisson of dread suddenly shivers through her—if she gets up, everyone will see

her "grapes" as her twin put it, the bumps in her shirt that she hadn't really paid any mind to or cared about before. But all that has changed now, and she feels so naked it's terrifying.

She shakes her head, and tries so hard to will the tears away but they spill again anyway.

She sees her father exchange a look with her teacher, which only adds to her mortification. She tucks her head back into her knees, holding tight to her legs.

"Then how about a piggy back ride?" her father offers. "Will ya come with us to the car?"

Atsumu lifts her head,

tentatively. If he carried her, then his tall, wide back would be like a shield, and no one would see. She swallows, and then nods.

"Good. Okay." He comes over and kneels down so she can climb onto his back, arms around his shoulders. She holds on with her legs, and he tucks his

big hands under her knees for support.

"Alright kids, let's go." They get to the car, and the teacher sees them off. When they're home, Atsumu crosses her arms over her chest and dances impatiently while their father unlocks the door. As soon as it's open, she dashes inside

and climbs up into her top bunk, bundling her blankets around her and over her head. She holds very still, thinking Osamu will come in too and bother her, but he and their father go into the kitchen to make dinner and Atsumu breathes a bit easier. Soon enough, her feelings

bubble back up and she stuffs her quilt into her mouth to muffle her sobs. She cries hard, with gusto, about how unfair it is that her body's like this. That they're not the same any more. That it's only going to get /worse/ because the other boys are going to tease her now too.

That she's probably going to have to get a bra, and their mom's at a work conference until next week, so how's she supposed to get one? It's all /so much./

She drifts off a couple of times between cries, but she's just gotten into another jag when Osamu comes in and blurts,

"Dinner's ready!"

Atsumu sobs silently, shaking under her covers. Who could possibly eat dinner at a time like this?

"Oi, didja hear me?"

"I heard ya!" she screeches. "Don't want any, so go away!"

A beat. Then, "Are ya /still/ cryin'?" His voice is incredulous.

"Course I am!" Atsumu yells, sitting up and uncovering her face, which she imagines looks horrible by now. "Yer so insensitive, ya jackass, an' I hate ya! Get out of here now!"

"I only asked if ya were cryin'!" Osamu rolls his eyes. "What's so insensitive 'bout that?"

"God! Leave me alone already! I hate ya and don't wanna see yer face!" Atsumu shouts, flopping back down in her protective cocoon.

Some minutes of silence pass, and then she hears the door close. Thank god—he left. She takes a shaky breath and exhales.

Then the wood of the bed

frame creaks and she can tell Osamu is climbing the ladder to her bed.

"Whatcha think yer doin'?" Atsumu shouts, head craned on her neck to see Osamu looming over her.

"C'n I come up?" he asks, gesturing for her to make room.

"No!" she snaps. "Go away!"

"C'mon, Tsumu,

don't wanna fight with ya any more."

"Yeah well too bad!" Atsumu huffs, turning back to the wall.

/"Move,"/ he insists, pushing on her back. "I wanna talk to ya."

Atsumu growls through her teeth and scoots over enough for him to get in the bed with her, settling on his side.

"Ya got 2 minutes before I drop ya over the side," Atsumu warns.

"Jeez, yer in a mood."

Atsumu elbows him in the guts. "An' who's fault is that?! Yer always pickin' on me an' I hate ya—"

"Stop sayin' that!" Osamu cuts in, voice frustrated. "I don't wantcha to hate me."

"Well tough!" Atsumu huffs.

Osamu huffs too. "An' I don't like it when ya cry like this, neither."

This of course makes her tears start right up again, and Atsumu bites her lip, sniffling. "Yeah well, s'yer fault, Samu. Yer mean."

Osamu tsks. "Don't think I was /that/ mean."

Atsumu gasps aloud, tears filling her vision. "Were too! Ya called me ugly! An' ya /pinched/ me! Yer horrible!"

"Wait I never called ya ugly!"

"Ya said I had grapes! Nobody wants grapes—grapes're ugly!"

"No, no, no," Osamu scoots closer, "Ya got it all wrong—"

"Howzzat?!"

"Arrrrgh!" Osamu groans, clasping Atsumu to him with both arms. "Listen! Yer not ugly I never said that okay? Yer not."

"Ha, yeah right," Atsumu sniffles. "Yer just sayin' that cuz yer in trouble."

"Shut up! I'm not!" Osamu thunks his forehead against the back of Atsumu's head.

Atsumu purses her lips, brow furrowed. "Either way, yer /mean."/

"Fine." Osamu exhales on her neck. "But it's cuz yer cute."

It's so absurd, Atsumu laughs. But then the sense that he's just saying things to make her laugh—or stop crying—and doesn't really mean them hurts all

over again and the tears continue leaking over her cheeks. She's able to keep silent, but she can't help shaking.

"Wha—yer /cryin'?!"/ Osamu says, shocked, and Atsumu lets out a half-sob.

"Jus' quit lyin', Samu, it's the meanest," she whimpers.

"But I just said yer cute!"

"Don't mean much when I know yer lyin'!" Atsumu snaps.

"Ain't lyin', Tsumu!" Osamu retorts, squeezing her around the blankets. "God, yer just not listenin'!"

"Ha!" Atsumu barks a laugh. "Say somethin' ya mean fer once and maybe I'll listen to ya!"

"Fine!" Osamu growls.

"Fine!" Atsumu replies.

No one says anything for a while, and Atsumu just lets the tears fall where they may, so many emotions pulsing right under the surface of her skin that it seems like one more barb and she'll just spill everything out until there's nothing left of her.

"Tsumu," Osamu murmurs into her short hair.

"Hmm."

Osamu squeezes her, but it seems more for his sake than for hers.

He clears his throat. "Tsumu. Yer cute."

"Hah?"

"Said yer cute!" he huffs. /"Cute!"/

Atsumu holds her breath. What?

When she doesn't say anything, Osamu

fidgets, making exasperated noises.

"Yer cute," he repeats, rushing onward. "All'ya, like yer d-dimples. S'cute. Also when ya set for yer team, ya look so happy. S'cute. E-everythin' 'bout ya s'cute, Tsumu."

Atsumu's cheeks heat up. Now she's the one fidgeting. "Ya mean that?"

Osamu nods into her hair. "Yeah. Really mean it."

She's not sure what to say, but she's definitely feeling a lot of new things. Like how relieved she is that he thinks she's cute. Like how much she wants to be special to him. Like how he's already so special to her.

Before she can come up with a reply, Osamu does something else. He hugs her tight to him, and then she feels a kiss in her hair, on the side of her head near the top of her ear.

"Don't hate me, Tsumu. I hate when ya hate me."

She lets out the breath she'd been holding, and

relaxes into his arms. "I don't hate ya, Samu. Not really."

"Good."

"Just /don't/ tease me like that again. 'Kay?"

"What, ya mean about yer grapes?"

"Samu!" Atsumu makes affronted noises while Osamu chuckles.

"Wouldn't dream of teasin' ya 'bout yer cute little grapes—oof!"

Atsumu takes some satisfaction from the noise of her elbow landing square in Osamu's stomach, which helps with the way her cheeks are steaming.

"Damn, sis, yer brutal," Osamu croaks.

"Serves ya right!" Atsumu scolds. But there's a half smile on her lips and her tears seem to

have stopped for the moment.

"Yer cute but..."

"But what?" Atsumu cranes her neck around, eyebrows raised.

Osamu smirks at her, winking with his good eye. "Hope ya get even cuter when yer grown up an' graduate to plums, peaches, or even melons—"

"SHUT UP!!"

//

#nsfw

Fast-forward to sophmore year of high school. Atsumu has indeed graduated from the grapes of her youth. Her figure has been blessed with a perfectly luscious pair of breasts the size of grapefruits.

Osamu /adores/ them.

He adores the rest of his sister too—her long blond ponytail fixed high on her head, the slim arch of her neck, the slope of her shoulders, the curve of her spine, how her waist tapers to meet the swell of her hips, the firmness of her ass and the strength of her glorious thighs.

cw: mentions of underage ranging from elementary to high school from this point <3

But since they were kids, there's always been something special about her breasts. How she'd finally let him up in her bed to prove his words from before were true, that he thought /all/ of her was cute. How he'd asked if he could see her chest, touch her a little, if she wanted.

How she'd wanted a kiss first. /So cute./ So he'd kiss her, as many times as she wanted, and then she'd squirm a little but eventually she'd lift up her shirt and show him her grapes.

Osamu didn't really know what to do, only that he /wanted/ to see and touch her and it made

his belly hot to brush fingers over her skin. He loved to watch her nipples tighten up, the both of them marveling at her body's reactions. Then her smaller fingertips coaxing his nipples to do the same, only this was not quite as exciting for either of them, just amusing.

He always keeps the focus on her, visiting the top bunk when he picks up on her interest. He monitors the slow, steady swelling of her chest. How sensitive she gets, especially once she starts her monthly cycle. How she starts wanting to be touched elsewhere, and he's only too

willing and eager to help her learn where and how she finds pleasure. Bringing her off with his fingers, his mouth. /Both./ Massaging her tits while they watch movies on her tablet, hushed under the blankets. Pulling her leg over his hip so he can tease her until she has to bite

his forearm to keep their parents from hearing when she comes, bucking against him for what seems like forever.

/So cute./

His hands can tell the subtle changes in her hips, her thighs, but she's not the only one changing. He outgrows her by four inches in one summer, gangly

like a beanpole for an agonizing year before he starts to fill out, get broad in the shoulders and thick with muscle.

It's sophomore year now and he towers over her by a head, can tuck her full height right under his chin, and he's probably not done growing yet.

Their size difference is /intoxicating./

Her hands are so small on his pecs, braced as she rides him in his bunk, his cock deep in her ass.

His hand covers her whole asscheek when she's laid across his lap for a spanking, whimpering as he paints her with handprints.

She's strong but he's stronger, and it's such a rush to fuck her against the wall or in the shower, lay her out on the dining table with her legs over his shoulders, or bend her over the back of the couch.

There's nothing they don't know about each other's bodies, be it touch, smell, or taste—except for one thing. They /are/ siblings, well aware of the taboos they break in body and heart, the secrets they keep.

But from the beginning, they agree there's one thing they /won't/ do:

Risk the chance of pregnancy.

Even combining different methods of birth control isn't completely safe, so they won't chance it at all. They agree so strongly on this point that they don't even have to discuss it.

Instead, they do just about everything else whenever they can,

and however they want.

What Osamu wants right now is to stand Atsumu in front of her dressing mirror, and pull up her uniform skirt, then pull down her panties and look over her shoulder while she gives him instructions on how to get her off, telling him exactly what she wants.

Not that he always listens, mind, because she also likes to be edged until she cries, and having her panting and frustrated and begging in his arms is such a beautiful thing.

He kisses her tear-stained cheeks and then pushes her over the edge, holding her upright when her knees

give out.

"Yer mean," she whispers, sagged against him but smirking in contentment.

"So ya say," he chuckles, pinching her nose and brushing the hair from her face.

"I hate ya," she teases.

"Liar," he scoffs. He kisses her softly, then again with all the possessiveness

in his heart.

He fixes her a snack while she showers and gets in her pajamas. After eating she joins him in his bunk and they get settled in for the night: extra pillows for her, and her pillows for /him./

Osamu rubs his face over her clothed chest, nosing the peaks

of her nipples and making Atsumu giggle. He grins, play-growling and burying his face between her grapefruits to hear her laugh.

"Yer cute," he says, inching her shirt up.

"So ya say," Atsumu replies. She guides his hands to push the fabric up and over her tits.

"The cutest," Osamu mouths into her left breast, closing his lips around her nipple. He holds her right breast in his left hand—it fits perfectly in his palm, like she was /made/ just for him.

Atsumu combs fingers through his hair as he suckles and caresses her, this act

that relaxes them right into slumber as part of their long-established nightly routine. God, he loves her so much it's insane.

"Seriously, Tsumu, yer the cutest," he tells her, kissing across the swells of her breasts from one to the other.

He glances up to find her cheeks

glowing red, lip caught between her teeth.

She musses his hair into his face. "Shut up an' sleep, Samu."

He kisses her goodnight, and settles against her chest, mouth and hand keeping her grapefruits comfortable and warm until morning.

💓

@threadreaderapp unroll please