How Using My Oppai Skill to Enlarge My Sister’s Breasts Led to Building a Harem - Chapter 12

Chapter 12

My girlfriend Satsuki-chan is a famous SNS influencer and magazine model. Naturally, she’s often at photoshoots, and today she’s at a beach for a bikini shoot, exuding even more mature allure than usual.

Why am I at her shoot? She invited me to hang out at the beach afterward.

“Looking good, Satsuki-chan! So cute today~”

The camera focuses on a stunning girl in a daring bikini—Satsuki-chan. Flawless, dewy skin, perfectly dyed blonde hair, a face that turns heads, and a body far beyond her middle school years.

Despite modeling for a teen magazine, Satsuki-chan loves revealing outfits like bikinis and dresses. Her influence on other girls makes her shoots as professional as a gravure idol’s.

“She’s got proportions beyond a middle schooler,” her manager says to me.

“Haha, yeah.”

Our relationship is public, so my presence at her shoots is fine, but since Satsuki-chan openly talks about our physical relationship, it’s a bit awkward with her female manager.

“…Use protection, okay?”

“Of course.”

She clearly knows what young couples do at the beach. Feeling complicated, I watch Satsuki-chan strike sexy poses for the camera.

…

“Sorry to keep you waiting, darling♪”

“Good job, Satsuki-chan.”

The elegant model transforms back into an age-appropriate girl, clinging to my arm.

“Hey, let’s go on a date!”

“Sure, we’re at the beach, so let’s have fun.”

“Yay!”

The beach is reserved for the shoot, and the adults have returned to the hotel, leaving us alone.

“It’s off-season, so the water’s cold.”

“Hehe, I brought a beach ball♪”

“Nice! Let’s play over there.”

We start playing with the ball on the autumn beach, still under blazing sunlight.

“Here!”

“Yo!”

Satsuki-chan claims she’s unathletic, but she’s not bad—just had tough competition.

(Still, they’ve gotten huge…)

Each toss makes her white oppai jiggle, burunburun♡. It’s hard to believe this perfect beauty is my girlfriend.

“Here it goes!”

“Ah…!”

I was too distracted by her breasts. The ball falls behind me, rolling away.

“Geez, darling, staring at my breasts too much.”

“Huh, how…!?”

“Hehe, your dick’s hard♡”

Satsuki-chan giggles, eyeing the bulge in my surf shorts.

(My lower half’s getting harder to control.)

Even alone, I’m fully erect outdoors. Despite loose shorts, my ever-growing cock is impossible to hide.

“Can’t go home like that, huh?”

“Uh, yeah…”

“Hehe♪ Anything you wanna say, darling?”

She unties her bikini top, letting it fall.

“C’mon, what do you want?”

“I… want to have sex with you, Satsuki-chan…”

“Sex outside? Someone might see~”

She sways her bare, beautiful breasts, tempting me.

“Behind those rocks, no one’ll see!”

“Wanna do it outside that bad? You’re such a perv, darling.”

My brain, ruled by my crotch, can only think of sex.

“Yeah, I can’t wait to fuck you right now.”

“Ahn, that makes my heart skip♪ You’re so dreamy, darling…♡”

Blushing, she says so.

…

“Let’s strip♪”

We get fully naked in broad daylight, facing each other.

“Haha♪ It’s so hard~”

“Your nipples are hard too, see?”

“Kyan♡ Geez, your touch makes me feel so much…”

Touching each other’s sensitive spots, her face turns dreamy, toron, our lust building.

“I’ll lie down.”

“Thanks, darling♪”

I can’t let her perfect skin get scratched, even on sand. I lie back in a good spot, looking up at her.

“Wow, your dick’s pointing straight up. It’ll get sunburned~”

“That’d be bad.”

“Hehe♪ I’ll cover it with my pussy. —Nn… ha♡”

Straddling me, she aligns my cock with her pussy and lowers her hips.

“Aaan! It’s going in…♡ Feels bigger than usual…♪”

As lovers, we fuck every weekend, knowing each other’s bodies well. But I haven’t told her I’m also having intense sex with other girls, my cock growing daily.

Zunyuu♡ — Paan♡ Paan♡ Paan♡ Paan♡

“Ah♡ Ah… ah, ah~♡ So good, feels amazing♪”

“Fucking this hard outside… first time since our first~!”

“Kyan♡ You remembered, darling…”

Our first time was in a secluded park, hidden, without this freedom.

“Of course! I love you, Satsuki-chan!”

Paan♡ Paan♡ Paan♡ Paaan!

“Nhu♡ I love you too, darling♪”

“Haa! Haa! Haa! Aaa!!”

We’re lovers, after all. Satsuki-chan’s precious to me, love surging from deep within.

“Ah, so good♪ Nhaa, coming outside♡”

“First shot, here it comes!!”

Our aroused bodies hit their peak fast. Semen surges from my balls, erupting deep in her pussy.

Dopyu♡ Byurubyururu♡

“Aaa…♡ My pussy’s coming… ah!~~~♡♡♡”

Our genitals pulse, embracing each other. Staring into her eyes, we savor the climax.

“Haaa… the breeze feels nice…”

“Haha, better than sex?”

“During sex♪”

I teased, but I felt the same. The cool sea breeze soothes our heated bodies.

“Darling, you can keep going, right♡”

“Yeah, as many times as you want.”

My stamina grows with each fuck, my sperm production speeding up. Normal sex? I recover mid-act.

“Till night, then?”

“If you don’t collapse.”

“Hehe♪ You’ll collapse first♡”

We fucked on the beach until dark. Back at the hotel, her manager’s cold stare was, well, charming.

※

I’m still massaging Nao-chan’s breasts. After loosening her growing oppai, Yukino thanks me with sex.

Pachun♡ Pachun♡ Pachun♡ Pachun♡

“Aan♡ Thanks for taking care of Nao… Nhuun♡”

“If this is the thanks, I’m all for it, Yukino!”

“Ah, no… saying that makes me love you more…”

Paan! Pan♡ Pan♡ Pan♡ Pan♡ — Pachun♡

“Ah♡ Ah♡ Ah♡ Love you♡ Love you so much, I’m going crazy…!”

“I love you too, Yukino!! Haa, haa…!”

Pan♡ Pan♡ Pan♡ Pan♡ Paan♡

“Lover sex♡ The best♪ So happy…♡ Ahn!”

Today, Yukino and I had loud, passionate love-making, echoing to the next room.

※

<Nao’s Perspective>

I have an older sister two years my senior. Yuki-nee’s always protected me when our parents scolded me.

“Nao can do great things if she tries. But no violence, okay?”

The honor student sister and the rough sister—guess who our parents favored. But I never resented Yuki-nee; I loved her too much.

Then, one day, she changed.

“Nao—I got a boyfriend…”

“What…? Yuki-nee, a boyfriend…?”

“He’s super cool♡”

Her eyes were heart-shaped. Sure, she’s cute, but never popular. Too serious, she never fit in, keeping friends at a distance.

(What kind of guy…?)

A foggy unease settled in my chest. But if she’s happy, I held back.

…

“How do you get piercings?”

“Huh? Wait, Yuki-nee, holes in your body?”

“Yeah… but it’s trendy.”

“No way, that’s bad…”

“Muu, it’s none of your business!”

Her sudden anger stunned me. She seemed desperate, pushing herself.

(Could it be… that boyfriend?)

No doubt. That boyfriend told her to pierce herself to suit his tastes!

“Unforgivable… I’ll kill him…”

My vision went red, focused only on beating that scum.

“I wanna meet Yuki-nee’s boyfriend. Bring him over.”

“Huh? Um, sure… but will he come?”

“Just once.”

“Okay, I’ll ask tomorrow.”

A boyfriend who won’t visit her house? She’s being played. Convinced, I hid a metal bat in the living room curtains.

I’ve never lost a fight, even against boys, but just in case.

(Come quick. I’ll make you regret it…)

Luring the so-called boyfriend, I screamed at the guy who showed up the next day.

“You’re the guy who seduced Yuki-nee!!”

I grabbed the cowering guy’s collar, ready to choke him. As I tightened my grip—

“Nao!! Stop!”

Paschin! Yuki-nee smacked my head.

Her slender arms didn’t hurt my tough self, like a kitten’s punch. But Yuki-nee, who’d never been violent, hitting me was a shock.

…

Turns out, the piercing was her flashy new friend’s idea, not her boyfriend’s. He was a saint compared to Yuki-nee, treating illnesses for minimal pay. I understood why she was smitten.

(Ayaka-nee’s savior…)

I’d done something awful to a family benefactor.

Feeling mortified, I started calling her friendly boyfriend “Onii-san.” He had another girlfriend, and Yuki-nee knowingly became his second.

(Relationships are so complicated…)

It was an adult world I didn’t get.

Then, talk turned to breast size.

“Want me to make yours bigger?”

Ridiculous, but Yuki-nee’s breasts had clearly grown in a month. She confidently said massages improve blood flow, enlarging them.

(Refusing feels like doubting Yuki-nee…)

“Just breasts… please…”

So I got Onii-san’s massage.

…

The result was unreal. I saw heaven. His hands were special, utterly professional. The pleasure knocked me out, and I woke in my bed.

“Ugh… why was I… asleep…?”

My brain foggy, I heard Yuki-nee’s moans.

‘Thrust harder… break me~~~♡♡♡’

Her voice, fully female, mixed with the bed’s creaking screams.

They’re having sex. Realizing this, I stumbled to the wall, eavesdropping.

(Incredible… the sound of flesh colliding. Yuki-nee gets this wild during sex…)

Thinking of the older two making love, my hips tingled, my pussy went jun♡, oozing sticky juice.

(No, no… I can’t do this to Yuki-nee…)

But my fingers moved to my dripping pussy, stirring it, kuchuri♡.

“Hauu…♡ ~~~♡♡♡”

One stroke, and I climaxed.

(No, no, no… n-no~~~♡ Uuu~~~ah♡)

Kuchu♡ Kuchu♡ — Kuchukuchukuchu♡♡♡

“Haa♡ Haa♡ Haa♡ Can’t stop my fingers…♡♡♡”

Eavesdropping on the lewd sounds, I frantically rubbed my pussy.

Kuchukuchukuchu♡ Pyu♡ Pyupyuu~~~♡

“Haan♡ Coming… coming~~~♡♡♡”

‘Yukino! Coming inside!!’

‘Ah♡ Ah♡ Coming in my pussy~~~♡ Haaan…♡’

‘Yukino, you’re so cute, chu.’

‘Chu, churu… chupa♡ Nfufu~♪’

Yuki-nee’s kissing Onii-san sweetly, like in manga or dramas.

(Jealous… jealous, jealous… so jealous~~~♡)

Kuchukuchukuchu♡ Pushi!

“Ah! U~~~, ahh~~~♡♡♡”

I came with a pathetic moan, my vision warping from unprecedented pleasure. Dizzy from oxygen deprivation, I leaned against the wall.

‘Let’s fuck more♪’

‘Yeah, I’ll pamper you more.’

‘Yay~ C’mon, put it in~~~♡’

While I struggled to breathe, they started again.

“Not fair, Yuki-nee… how many times…?”

Even saying that, my fingers reached for my soaked pussy.

…

Onii-san massaged me a few more times. Each time, hearing Yuki-nee’s moans made my body ache uncontrollably.

(I can’t take it… Sorry, Yuki-nee…)

I sent Onii-san a message.

‘I need to talk. Can we meet somewhere Yuki-nee won’t know?’

Done. If he refuses… I won’t think about it.

Ping

A reply.

‘Sure. My clinic okay? It’s at—’

I clenched my fist secretly. Yuki-nee might hate me, but my body can’t suppress this ache anymore.

“Wait for me, Onii-chan♪ I’m coming!”