How Using My Oppai Skill to Enlarge My Sister’s Breasts Led to Building a Harem - Chapter 4

Chapter 4

I ended up in a physical relationship not only with my sex friend Satsuki-chan but also with her mother, Mizuki-san, after meeting her at their house.

Since then, I’ve found myself making excuses to visit the Sasahara household and have sex with both of them.

“Nnn♡ So good, boyfriend-kun, you’re really getting the hang of handling women, ahn♡”

“Fuh, ha, ha, kuh!!”

Satsuki-chan was lying on the bed, breathing heavily, cum dripping from her pussy after her climax. Right beside her, I was having sex with Mizuki-san.

“Hey, just marry Satsuki♪ Then we can pamper you forever.”

“I can’t marry yet, ugh!”

“Ahn♡ Then get engaged, that’s fine, right?”

Paan♡ Paan♡ Paan♡ Paan♡

“Nnhiii♡ Your cock’s so good♡ Thrust harder♡♡♡”

It’s always like this.

Mizuki-san’s taken a real liking to me, urging me to marry her daughter every time we have sex. But age-wise and emotionally, I’m just not ready for marriage.

(I know I’m cheating, but Ai’s the one I love most.)

Even while having cheating sex, my cute sister’s smile flashes in my mind. I don’t want to hurt Ai—she’s my one and only, my soulmate, the most precious girl in the world.

“I’ll tease these naughty oppai too.”

Dodging her words, I kneaded Mizuki-san’s soft, marshmallow-like oppai, munimuni, stimulating their pleasure nerves while testing if I could repair her Cooper’s ligaments to prevent sagging.

(They’re feeling a bit firmer than before.)

My hands are like precision tools when it comes to oppai. From their sensitivity, I could tell the ligaments’ stretching had not only stopped but was slightly reversing.

“Don’t rub my oppai… nnn, nnuuu~~~♡ Haaa♡♡♡”

Mizuki-san climaxed from her breasts, twitching pikupiku. Her sensitivity might’ve improved too.

“Your breasts are getting firmer, Mizuki-san.”

“Oh, you can tell? Your hands are really something…”

I’d told Mizuki-san about my special hands. She’d always wondered how Satsuki-chan’s breasts grew so fast, so she seemed to half-believe me.

“If you became my son-in-law, I’d…”

“Mizuki-san…”

Her heated gaze met mine. We didn’t say it, but the age and status gap was too wide. Those words were probably the most she could express.

Feeling a pang in my chest, I creampied the beauty before me. In that moment, my affection for Mizuki-san drowned out the pain…

That day, I fucked this mother-daughter duo over and over until my balls were completely drained.

…

“Hey, boyfriend-kun, could you check out the girls’ breasts at my shop?”

“Huh?”

Exhausted and sprawled on the bed after going at it, Mizuki-san made the request.

“Mama, your shop’s where adults go to have sex. Onii-san wouldn’t like that, right?”

“Uh, well… it’s not that I’d hate it, but I’ve never been…”

I mean, I’m too young to get in, and I don’t have that kind of money. Tough question.

“You wouldn’t be going as a customer, so it’s fine, right?”

“Is it? …Guess if I don’t get caught.”

I’m a bit skinny, but plenty of adults my size go, so maybe with a disguise, it’d be okay. And so, I ended up examining oppai at a high-class escort agency.

※

“Uh, thanks for having me…”

A few days later, I visited the upscale escort agency where Mizuki-san worked.

“Oh, Mizuki-san, is this the guy?”

“Ufufu, yup. He’s the one who fixed my breasts.”

Mizuki-san, in a luxurious dress showing off her deep cleavage, puffed out her chest.

(I’ve rubbed them a few times since, and they’re back to twenties-level firmness.)

Her once-sagging breasts, which she’d been shy to show off, now formed a stunning valley of plump mounds.

“They’re so beautiful… It’s like my idol Mizuki-san is back. I’m so happy!”

Misa-san, her junior, grabbed Mizuki-san’s hand. Apparently the shop’s number two, Misa-san had been mentored by Mizuki-san since her rookie days and was thrilled at her “comeback.” I was starting to feel the pressure of their expectations.

“Let’s have the girls who’ve finished their shifts get checked, shall we?”

“Y-Yes…!”

“No need to be so nervous, sweetie.”

Misa-san’s gentle smile eased my tension. Her soft, beautiful face made mine flush red. Mizuki-san’s gorgeous, but Misa-san’s a stunner too. I might’ve walked into something wild.

…

“Ahn♪ You’re so good for a young guy… nn, haa♡”

I was massaging the ninth woman’s breasts. She was self-conscious about her small chest and wanted them bigger.

Women’s oppai are all unique. No two are the same, each with its own ideal shape. My job was to get them as close to that ideal as possible.

“Stimulating deep like this helps the breasts grow.”

I explained, pressing her modest breasts, kunikuni♡, with my fingers.

“Nnn… yeah, it’s getting hot inside… ahn♡”

Another woman moaned seductively as I massaged her, my groin swelling with pent-up desire.

(Just rubbing oppai is making my crotch ache…)

My pants were bulging, my swollen cock rubbing painfully against the fabric. But I still had one last job—Misa-san, the first woman I’d met here.

“Please, do your best, sensei.”

“Uh, yes… I’ll try!”

I’m no doctor, but they seemed to trust me. Misa-san, true pro, bared her ample breasts without a hint of shame.

(Wow… so beautiful… those tan lines are super sexy…)

Her tanned skin bore bikini marks, with H-cup-ish breasts and perfect pink nipples—a flawless, youthful body at its peak.

(Just looking, I can’t see anything wrong…)

Looks alone don’t tell the full story, especially with internal ligaments that stretch over time. “Let me check,” I said, sinking my fingers into her lush breasts.

Munyuri♡ My ten fingers sank into her soft flesh. For an oppai lover like me, the feel alone was worth the trip. But as I lifted the heavy mounds with my palms, I noticed something.

“The left and right are slightly uneven… Does your right shoulder ever feel stiff?”

“Huh? Yeah, I’ve been bothered by right shoulder stiffness. How’d you know…?”

“Breasts aren’t perfectly symmetrical. Even a small weight difference can throw off your balance.”

I’d always considered balance when enhancing women’s breasts. Weight differences might not show visually, but over time, they affect posture.

“I’ll adjust it. I’ll go a bit deeper.”

“Okay, please. Nn… haa, uun♡”

I slid my fingers deep into the base of her large breasts, working the core.

“Auh… your fingers are going inside my oppai. It’s… hot inside♡”

“Your breasts are big, so I need to go deep to stimulate them. Does it hurt?”

“Nn… it’s fine, haa♡ My oppai are tingling…”

As I moved my fingers to stimulate deep, I could feel her body heating up.

“Ah, no… my nipples are getting hard…♡”

“That means it’s working. I’ll go a bit harder.”

“Ah, uuu♡ No… any more and, hauuu~~~♡”

Misa-san started twitching, pikupiku, moaning seductively. My massage worked well, reaching the core of her breasts. This should balance them out.

“All done, Misa-san. How’s the shoulder stiffness?”

“Wow… it’s really better.”

“It’s temporary for now, but a few sessions should fix it permanently.”

Breasts don’t grow instantly; it takes consistent treatment.

“But there’s one problem…”

“Huh? Something wrong?”

“Yup, right here♡”

She lifted her breasts, showing off her rock-hard nipples.

“They’ve been aching since earlier…”

“Uh, that’s…”

“You’ve gotta finish the treatment properly♪”

“Y-Yes!”

Misa-san shifted from professional to a sultry, wanton woman, exuding mature allure. Inexperienced as I was, I fell for it, diving into her body with raw desire.

…

Pachun♡ Pachun♡ Pachun♡ Pachun♡

“Ahn♡ So good… swing your hips harder♪”

“Misa-san! It’s amazing, so good!”

I was fucking her pussy raw in missionary. As the shop’s number two, her meiki rivaled Mizuki-san’s, with soft folds wrapping around my cock, nyurunyuru, with every thrust.

“Fufu♪ So, whose pussy feels better, mine or Mizuki-san’s?”

“Kuh, aaah! I… can’t choose…”

Both Mizuki-san and Misa-san were top-tier women with incredible bodies and skills. Sex with them was pure pleasure—no way I could rank them.

“Hmm, really? I had high hopes since Mizuki-san’s so fond of you…”

“Eh, uwa!”

Misa-san sat up, my cock still inside, shifting to cowgirl.

“A big cock alone won’t satisfy Mizuki-san, y’know?”

“Ugh… what’s that mean…?”

Pachun♡ Pachun♡ Pachun♡

She rode me, her big hips grinding my cock, goshigoshi, like she was dominating me.

“I’m gonna test if you’re worthy of Mizuki-san♪”

Paan♡ Paan♡ Paan♡ Paan♡

“Guhaa…!”

“Here, here, work those hips harder. You’ve got a great cock, so use it♪”

Her upper mouth spoke sweetly, but her lower one was merciless, squeezing my cock and demanding cum. Under her assault, I instinctively reached for her oppai to fight back—

“That hand’s cheating… You’ve gotta please me with your cock now.”

She gently grabbed my hands, stopping me.

Then, like doing squats, she slammed down, dochun♡ dochun♡, onto my groin.

“Already gonna come? Nope, you gotta try harder… nn, nn♡”

“No way… I’m gonna, come!”

“Fufu♪ Fine… if you’re gonna come, thrust as hard as you can, go♡”

Her pussy clamped down, kyuu, squeezing my cock perfectly. I thrust wildly as she urged, pounding with breakneck speed.

Paan♡ Paan♡ Paan♡ Paan♡ Paan♡

“Ohhh♡ You can do it… so good, more, more♡”

I thrust with all my strength, bouncing my hips like a jackhammer.

“That’s it♡ Pound me with that huge cock♡”

“Aaa…! I’m really at my limit!”

Dochun♡ Dochun♡ Dochun♡

“Nnn♡ Haa♡ So good, I’m gonna come… nhaa, yes♡”

“I’m… coming!”

“Ahn♡ Coming, coming~~~♡♡♡”

Misa-san climaxed, her pussy walls writhing around my cock. The intense sensation made me shoot cum with incredible force.

“Ahn♡ So hot… your big cock’s shooting such thick cum♡”

I trembled, unloading dobyudobyu into her pussy, semen overflowing from our joined parts.

“Haa haa…♡ That was great. No wonder Mizuki-san picked you.”

She whispered sweetly in my ear, her allure completely captivating me.

Then she said something unbelievable.

“Wanna go again♪”

“Huh…?”

“I heard from Mizuki-san you can go multiple rounds, right?”

Sure, I don’t usually stop at one, but this was Misa-san. I’d already emptied my balls.

“It’s fine, I’ll train you. Let’s exchange contacts later.”

Smiling, she squeezed my softening cock with her pussy and started moving again.

“I’ll make you a real man♪”

And so, I was milked dry until I was on the verge of collapse.

※

Ai’s Perspective

I have an older brother a year older than me. We’ve been close since we were little, always playing together. One day, he started rubbing my chest, calling it a “massage.” I was too young to understand, so I innocently went along.

“Here, I’ll make your oppai bigger!”

“Nn… ahh, Onii♡ My oppai feel good…♡”

Looking back, that was my sexual awakening. After that, I got hooked on the pleasure of touching my oppai, masturbating daily.

But it didn’t last. Once my breasts started growing, he stopped the massages. That melting pleasure was something only his hands could give me…

Since then, I couldn’t stop thinking about him. As we grew up and became more aware of sex, it only got worse.

So, I boldly asked him to rub my oppai again. He was surprised but, being an oppai lover, didn’t refuse.

Guni♡ Gunyugunyu♡ Guniii♡

“Haaan♡ Onii, that’s amazing♡”

His hands were incredible. My daily masturbation couldn’t compare. I became addicted to the pleasure, my heart pounding.

(Maybe… I love Onii.)

That’s when I realized my feelings. I kept trying to get his attention, but the thing with my friend Satsuki-chan made him depressed.

“But it worked out in the end, right?”

Now we’re mutually in love. Even if we can’t marry, I’m happy just being together.

But—

“Onii’s been acting weird lately.”

He used to fuck me anywhere in the house, but now he’s not as eager. His fashion sense has improved, and he’s been getting haircuts, caring more about his looks.

And then—

“Ai, I got some birth control pills. You can use them if you want.”

He’d gotten pills, which aren’t sold over-the-counter. I’d given up on them, but where did he get them? He just said “from a friend” and wouldn’t elaborate.

“Something’s definitely off…”

I decided to confront him.