How Using My Oppai Skill to Enlarge My Sister’s Breasts Led to Building a Harem - Chapter 20
Chapter 20
I found myself being confronted by my sister Ai about my cheating.
Returning home from the clinic, she was waiting, silently radiating pressure.
“Welcome back, Onii-chan. Dinner’s gone cold.”
“Ugh, sorry, Ai… Mom too.”
“It’s fine. You’ve been studying hard lately,” Mom says.
Our family’s laissez-faire, so no one worries if I’m late. But Ai’s different.
“Mom went to the trouble of cooking…”
“Yeah, sorry, Mom.”
“Come home earlier if you can.”
It seems like a normal family exchange, but—
“(I’m coming to your room later…)”
—Ai whispered behind me.
…
“As I said, Onii-chan, you know why I’m mad, right?”
True to her word, right after dinner, Ai storms into my room, pressing me.
“It’s about my cheating. I’m sorry for keeping it from you…”
“…”
“Ai?”
“It’s just cheating, right? You’re not actually in love with them, are you?”
“W-Why would you think that?”
I can’t say it’s not serious. The women I’ve been with are all captivating—I don’t see it as just a fling.
“‘Cause lately, Onii-chan… you’re getting cooler and cooler.”
True, I’ve been grooming better. At the Saionji estate, maids handle my haircuts and skincare daily. I work out, train, and Miyabi drills me on posture, walking, and manners.
“Keep your spine straight. No, the human spine curves in an S-shape…”
Miyabi’s lessons echo in my mind.
“Imagine your head being pulled upward while standing naturally.”
It’s second nature now. Even under Ai’s pressure, my posture stays firm.
“You’re growing up so fast, Onii-chan…”
“Ai…”
“It makes me… anxious…”
“I love you the most in the world, Ai. That won’t ever change.”
“Really?”
“Yeah.”
Ai’s my top priority. That’s no lie.
“Then tell me about all the women you’ve slept with.”
“…Okay.”
I end up confessing everything.
“Yukino-san, Riria-san, Nao-chan, Ayaka-san, Miyabi-san—huh. That many?”
“Uh, it just… happened.”
“How serious is it?”
A tough question. I could say I’m serious about them all, but since I’m not engaged, it’s just physical. I’m at a loss.
“You haven’t forgotten Satsuki, right?”
“Of course not. I love Satsuki-chan too.”
They had a rough patch but became best friends after overcoming it. Ai can’t stand me neglecting Satsuki.
“I’m your number one, right?”
“Yeah, you’re the top.”
“Then—how about you say that in front of all your flings?”
Ai’s demanding I expose our sibling romance in front of everyone. Stunned, I stare at her.
“You can’t?”
“—Fine. I’ll contact them.”
She’s serious, so I have to be too. Since tomorrow’s Saturday, I ask everyone to come to our house by noon.
…
The next morning, I sneak into Ai’s room, watching her sleeping face.
(Sorry, Ai, for being such a cheater…)
“Uun… Onii-chan, idiot…”
Muttering in her sleep, dreaming of me.
“I really am an idiot…”
Cheating despite having such a cute sister? I’m messed up. My lower half doesn’t listen around beautiful women, and that’s my biggest problem.
“But I gotta face it now.”
Muttering, I quietly leave her room.
…
By noon, everyone gathers in our modest living room: Ai, Satsuki-chan, Ayaka-san, Miyabi-san, Yukino, Nao, Riria—seven stunning women in one place.
(Everywhere I look, it’s beauties and cuties. If this weren’t a cheating tribunal, it’d be paradise…)
“Um, Onii-chan… you really did it with all of them…?”
“Y-Yeah.”
Ai’s voice trembles. The three her age are one thing, but Ayaka and Miyabi are clearly mature, elite beauties beyond her usual world.
Even Ai falters, at a loss for words. Satsuki takes over.
“Let’s start with introductions. I’m Sasahara Satsuki, third-year middle school, model.”
“Satsuki’s Onii… my brother’s girlfriend,” Ai adds.
No one’s shocked—she’s known as my girlfriend.
“I’m Saionji Ayaka. I met sensei at the clinic during treatment, and we grew close.”
Ayaka explains her abusive husband, her near-suicidal illness, and how I saved her. Everyone sympathizes, easing off on her.
But Satsuki has a concern.
“So, you’re not thinking of marriage?”
“No. The Saionji family wouldn’t allow our divorce…”
“Okay, that’s fine.”
Her inability to marry seems to satisfy Satsuki. Miyabi and Riria, being just physical, pass calmly, but—
“I’m Tsukihara Yukino, his classmate… and his second girlfriend.”
Satsuki reacts sharply.
“I’m his girlfriend.”
“Yes, so I’m… hoping to be the second…”
“…”
(My stomach hurts… Satsuki just learned about another girlfriend.)
“Fine, we’ll talk later, just us.”
“Yes…”
Pathetically, I can’t interject—anything I say would make it worse.
“I’m Tsukihara Nao, Yuki-nee’s sister, second-year middle school. I’m Onii-chan’s sister♪”
Ai, my real sister, snaps at this.
“I’m his sister. You’re a stranger.”
“We don’t need blood to be siblings. Step-sister, right?”
Nao’s unfazed by Ai’s intensity, boldly declaring herself my step-sister.
“No… I can’t accept that. Onii-chan’s sister is me—right?”
Ai looks at me, tears welling, ready to spill.
“…!?—Ai… Yeah, I was wrong.”
Making my sister cry? I’m a failure as a brother. Regret and pain flood my chest.
“Sorry, Nao. You’re adorable, but I can’t let Ai, my family, my most beloved girl, cry.”
“Onii-chan…”
“Onii…!”
My words shift focus to Ai. They now understand why she’s central here. I steel myself.
“I’m in love with Ai—my real sister.”
Even if this ruins everything, I won’t regret it. I can’t abandon Ai.
“Hmm, so Onii-chan loves his sister most.”
“Yeah.”
“Got it. That’s great♪”
Nao smiles happily.
“Why the weird look? I love Yuki-nee, and she cherishes me. It’s the same.”
“Even for romance?”
“Why not? You’re a guy and girl. If you fall in love, that’s that.”
Her words soften Ai’s tense expression.
“Nao-chan, right? Sorry for being harsh.”
“It’s cool~ Siblings should get along. If Onii-chan didn’t protect his sister, I’d be disappointed.”
In her world, a brother who doesn’t protect his sister is absolute evil. Did I make the right choice?
“But I won’t lose. I’m your step-sister, after all.”
“…Yeah. I won’t lose either. Onii-chan loves me most.”
Riria, the troublemaker, jumps in.
“Really in love as siblings?”
“What’s that mean?”
“Are you having sex?”
Riria smirks, prying out of curiosity.
“We are…”
“Really? Blood-related siblings having sex?”
“Look, Riria… Let’s drop it—“
“It’s fine. If you’re so curious, I’ll show you proof,” Ai cuts in.
“Sex proves it, right? We’re in love, so it’s no big deal. Right, Onii?”
Caught by Riria’s taunt, Ai declares we’ll have sex.
“Ai, don’t let Riria bait you…”
“Onii? I’m your number one, right?”
“Yeah.”
“Then prove it. Show everyone I’m first.”
Seeing Ai’s expression, I realize—she’s not baited. She wants to show the others.
“You can, right, Onii?”
“Of course.”
Her desire to be my number one breaks my reason. I’m smitten.
“We’ll do it in front of everyone, like always.”
“Yup♡”
I princess-carry Ai to the living room sofa, laying her down.
“You’re so cute, Ai.”
“You’re… so cool, Onii. Getting manlier every day.”
As I strip, her heated gaze locks on me. That look—
“Ai!”
“Kya!”
My bursting love makes me pounce on her mid-undressing.
“Onii… your hands are so naughty…♡”
“It’s ‘cause you’re too cute. Your boobs are so big now.”
Munyu♡ Guni guni♡ Muchii♡
I raised Ai’s breasts, molding them daily into perfect, balanced masterpieces. No matter how often I touch them, they’re mine—only mine.
“I know every inch of your body.”
“Aun♡ Okay, Onii… My body’s getting hotter…”
I unleash all my skills on her fully-developed, all-erogenous breasts.
Gyunyu♡ Nyuu♡ Purupuru♡ Gyuu♡
“Aa♡ Haa haa♡ Aanu♡”
“See, kneading deep into your boobs’ core…”
“Iii♡ That… I love it♡”
I slide all ten fingers along her pleasure nerves, pressing toward the center—a technique only possible because I know her breasts perfectly, delivering ten times the stimulation.
“Aaa… I’m gonna cum♡ So soon, I’m cumming…♡”
“Go ahead. Show your big brother your cute cumming face.”
“Nuu♡ Haa… Aa, cumming, cumming~~~♡♡♡”
Ai surrenders completely, climaxing without resistance.
(She looks so blissful. As blood siblings, our hearts and bodies connect.)
That’s what sets her apart. Ai trusts me 100%, accepting pleasure fully and showing it to me.
“Now it’s your turn to feel good, Onii.”
“Yeah, please.”
I’ll bare everything to Ai too. Aroused by her sexy form, I press my cock to her delicate lips for a blowjob.
Without a word, she naturally takes my glans, licking eagerly.
Juzozozo. Rero♡ Reroo♡ — Juzuzuzu♡
She softly kneads my balls, activating my sperm factory with perfect pressure, knowing my shape and size.
My high libido needs Ai’s morning blowjobs to calm my erection—it’s our routine. She caresses my cock and balls expertly, using lips, tongue, cheeks, and palate, sometimes swirling her tongue like a screw to stoke my pleasure.
“Amazing…”
“Looks like you’re feeling good, Onii-chan.”
“That girl’s better than me…?”
“Hau… Licking a man’s penis like that…”
“I’ve never seen such skill.”
The others start buzzing. Pleased, Ai glances at them, puffing her nose smugly.
“Here’s the usual, Onii.”
“Yeah, go for it.”
“Nfuu… Nyururu♡ Jururuuu♡ Jupo jupo♡”
Ai swallows my cock deep, performing a deep throat.
“Nn… Jubo♡ Jubo♡ Jubo♡ Njurururoo♡”
“Kuhaa…! It’s intense…”
No one knows my cock like Ai. Just as I know her body, she knows mine.
Sensing my climax, she speeds up, stroking my shaft rapidly.
“Nn, juppo♡ — Juppo♡ Juppo♡ Juppo♡”
“Aa… So good… My cock’s melting…”
“Nfufu♪”
Sucking my cock, she looks up with an angelic smile.
(She’s so cute. My sister’s definitely the cutest girl in the world.)
“Kuu…”
“Oni, jubu♡ Jubobo♡… Ready to cum? —Jururero rero♡”
She licks my frenulum. The sensation’s too intense, sending shivers through my hips.
“Ku… Aa!”
“Ihhy♪ Ahn… Nyururururu, Kapo♡ Fuu~…♡”
For the finale, she swallows my cock to the base. Despite its size, she takes it without gagging, her throat tightening, kyu♡, squeezing harder than any pussy.
“U, ooooh!!”
“Ngo♡ Ngu♡ Ngu, ngu…♡ Juro, Gogu♡ Gogu♡”
I shoot my semen straight into her throat, unable to hold back. A volume that’d choke most, Ai handles effortlessly, gripping my balls to demand more.
“Guo! Aa, it’s draining me… So good…”
No pussy compares to my sister’s mouth-pussy, crafted for me, draining my balls, byukubyuku♡, until my desires are spent…
Gokun♡ Nyururu, Puha♪ “Thanks for the meal.”
Ai swallows every drop without spilling, storing it all in her stomach.
Meanwhile, one blowjob drains all my semen, leaving my cock dangling pathetically.
“Amazing, Ai…”
“No way… She swallowed that huge cock…”
“Incredible…”
“Onii-chan, satisfied with one go…?”
“Hawawa…”
“Milady, stay strong.”
It leaves a strong impression on the women. But I know Ai best—she’s not done.
“Let’s do the real thing, Onii♡”
Saying so, Ai spreads her pussy wide, flaunting it to her rivals.
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