How Using My Oppai Skill to Enlarge My Sister’s Breasts Led to Building a Harem - Chapter 13

Chapter 13

I came to the clinic to hear Nao-chan, Yukino’s little sister, out about her concerns.

“No appointments today, so it’s perfect timing.”

Unlocking the clinic as usual, I step into a spotless interior, not a speck of dust on the floor.

“Ayaka-san cleaned again, huh? She’s such a help.”

Ayaka’s practically family, so I gave her a key. She cleans and restocks supplies without being asked.

“The break room’s spotless too.”

The break room has a nice bed, a gift from Ayaka. What it’s used for… well, no need to spell it out.

(I gotta do something to thank her…)

Maybe a nice accessory for a grown woman? But I don’t have the cash for anything fancy.

(Well, it’s not urgent. I’ll ask Ayaka what she wants next time.)

While sorting supplies and thinking this, I get a message from Nao-chan.

‘I’m here, Onii-san.’

My clinic has no sign, being referral-only, so Nao-chan must be lost.

“Sorry, sorry! Over here, Nao-chan.”

“Oh, Onii-san! Thank goodness.”

When I call out, she looks relieved and approaches.

(She seems… different today…)

“Can I come in?”

“Yeah, it’s small, but go ahead.”

“Excuse me.”

Entering, Nao-chan looks around, surprised.

“This is your room, Onii-san?”

“Well, I rent it, so not really mine… but I can use it as I like, so kinda?”

“Wow, so cool~♪”

She’s unusually close today, her breath almost brushing me as she talks.

(She’s making my heart race… Was Nao-chan always this cute?)

I always thought she was cute, but today she’s radiating an irresistible aura.

“S-So, what’s this about?”

“Um, can we do the massage first, like usual?”

“Of course, no problem.”

I start to lead her to the treatment table but reconsider.

“Treatment table or bed?”

“Bed, please♪”

Since we’ve always used a bed for her massages, I guide her to the break room bed, usually reserved for… well, me and Ayaka.

(Ayaka’s family, so it’s fine, right?)

This bed’s only been used for sex with Ayaka, but now it’s hosting someone else for the first time.

“Here you go.”

“Thanks, Onii-san. Nsho…”

Nao-chan strips to her panties, as usual, and lies on the bed. But today, her skin seems rosier, her body warmer.

“Let’s start. Relax, okay?”

“Okay. Ahn♡ It’s cold…”

“Oh, sorry. Same oil as always, though.”

“It’s fine. Um… can you make it stronger today?”

She’s used to strong massages already, but stronger?

“Stronger means touching different spots, you know?”

“Yeah, please♡”

“Got it. Here we go!”

And so, I begin Nao-chan’s massage.

…

Gyu♡ Munyu♡ Gunyuu♡ — Purun♡

“Haa♡ Haa♡ Haaa… Nn♡”

“How’s that? Your breasts are getting bigger, right?”

“Yeah, almost catching up to Nee-chan… Ahn♡”

Not just size—her breasts’ sensitivity has spiked. A mere touch makes her writhe like I’m hitting an erogenous zone.

“It’s working great, Onii-san. Haan♡ More… stronger, please♡”

“Alright, I’ll touch here then.”

I reach for the peak of her breast mountain—her nipples. My hands are so strong I’ve avoided them to prevent overstimulation, but to go stronger, it’s time to unlock them.

I trace her perfect pink areolae like stroking piano keys.

The effect is dramatic.

“Ah, haaaa…♡♡♡ My breasts… tingling…♡”

“Just hold on a bit.”

Shu♡ Shu♡ Surisuri… Kuni♡ Kuni♡

I rub her areolae in circles, keeping their perfect shape balanced with even stimulation.

“Hau♡ Hoo♡ Hoo♡ — Ohh♡”

“Seems to be working. Can you handle more?”

“Y-Yeah… haan! I can take it♡”

With her okay, I shift from circling to aligning my five fingers, targeting the ultimate erogenous zone—her nipples.

“Here’s the strongest… Here!”

“Nn! Giiii♡”

She screams, her body jolting like she’s been shocked, eyes wide open.

“Ohhh♡ My breasts… electric…♡”

“Hold on a little more.”

I twist the pink buds I’m pinching, kurikkuri♡.

“Ahuuu♡ That’s… too much…♡ Ohh♡♡♡”

She climaxes, trembling, breathing shallowly, hii hii.

“Almost at your limit?”

“No… don’t stop… finish it properly♡”

“You sure? You might pass out.”

“I’m fine… I can handle anything from Onii-chan.”

She gazes at me with her beautiful face.

“O-Okay… Do your best!”

I stand my fingers vertically, plunging into her large, soft breasts.

Gu… Nyuuu♡

“Uhaa♡ My breasts… crushed!”

“It’s okay, I’m stimulating inside now.”

I vibrate my fingers like a massager, shaking her breasts.

“Hii… Aaa♡ What’s this…♡”

“I’m stimulating all your breast meridians and nerves. I’ll speed up.”

My hand vibrates like a device, rippling her breasts from my fingers.

“Ohhh♡ Ohhh♡ My breasts… something’s opening…♡”

“Your whole body’s nerves are active. All your feel-good spots are opening.”

“My body’s… changing…♡”

Like a manga chakra opening? I don’t have breasts, so I can’t know, but opening meridians with my fingers is great for beauty and health.

“Almost done.”

“Oh♡ Ohhh♡ My breasts… too much…♡”

“You did great, Nao-chan.”

I gently stroke her drooling, cute face.

(I used to pat Ai’s head like this…)

I stopped as she grew up, but patting a cute girl’s head feels amazing.

“O-Onii-chan♡ …Onii-chan♡ Onii-chan♡”

“Nao-chan?”

She’s calling me “Onii-chan” now, not “Onii-san.” As a self-proclaimed siscon, that hits my heartstrings.

“Onii-chan, I love you… I really love you♡”

Her face is so cute, beautiful, sparkling.

My heart skips, dokun. Blood rushes to my head, and I can’t look away. Her sweat’s sweet scent invades my nose, burning my brain.

(So… cute…)

Her angelic “Onii-chan” pierces my heart in one shot.

(A sister besides Ai… No way…)

“Onii-chan♡ Love Nao too♡”

“Nao… chan… I…”

Ai’s face flashes in my mind. But I can’t not love this adorable “little sister.”

…

“Nao, spread your legs.”

“Nn, it’s embarrassing…”

“No sex without undressing.”

“Y-Yeah… okay…”

Her panties, soaked with love juices, are heavy. I pull them to her knees, observing her pink pussy.

“Nnu… it’s embarrassing.”

“It’s beautiful, Nao.”

Her labia are tightly closed, perfectly pristine.

“I’ll look inside.”

“Ah… you’re spreading it…”

Opening her pussy, I see her twitching vaginal opening and urethra.

“I can see your hymen.”

“Ah… ugh…”

“I’m taking your first, okay?”

“Yeah…♡”

To take her virginity, I press my cock against her untouched vaginal opening.

“It won’t hurt. I’ll cast a spell.”

“Spell?”

I massage her butt and thighs, stimulating pleasure nerves. Having opened her meridians earlier, this alone excites her.

“Here goes…!”

“Ah! Nnnn~~~!”

My glans pushes into her pussy, advancing. It hits her hymen but breaks through, buchibuchi, conquering her virgin vagina.

“Nnn♡ It doesn’t hurt… my pussy’s tingling♡”

“It’ll feel good soon.”

Her pain seems numbed; she feels no deflowering pain. Stroking her soft skin makes her twitch with pleasure.

“Look, I’m all the way in, Nao.”

“Ahaa♪ Onii-chan’s hitting deep…”

My cock’s tip touches her cervix.

“This is where your babies are made.”

“Ahn♡ Don’t grind there…”

“I’ll make you feel even better.”

I’ve located her portio and know I can make her feel good anytime.

“Leave it all to Onii-chan.”

“Ah… yeah♪”

I cover her body, moving my hips subtly to stimulate her portio.

“Ah♡ Ah♡ Ahh… so good♡”

Her weak spot is nearly identical to Yukino’s. Sisters’ bodies must be similar. My trained hips arouse her pussy.

Paan♡ Paan♡ Paan♡ Paan♡

“Onii-hyan♡ Ah♡ Ah♡ Ah♡ Amazing♡”

“Your pussy’s amazing too, Nao! Chu… Jururu…”

“Nchu—♡ Jururu, chu♡ Chupa…♡”

I suck her lips, drinking her honey-sweet, refreshing saliva, like premium fruit water, absorbing into my body.

Desire ignites in my hips.

Sucking her lips, jurujuru, I knead her breasts, caressing her body. Wanting this beautiful girl, my serious caressing begins, beyond massage.

“Nnn! Onii-hyan♡ Nuu~! N~~~♡♡♡”

Mouth sealed, body massaged, pussy fucked, Nao climaxes.

“Sisters belong to their brother, right?”

“Haa♡ Haa♡ Fue…?”

I stop my subtle thrusts, pinning her to the bed, raising my hips high.

Dochun! — Paan♡ Paan♡ Paan♡ Paan♡

“Ah♡ Ohh♡ Nhiii♡”

“Nao! Nao! Nao!!”

I pour my burning desire into my cock, piercing her pussy’s weak spot repeatedly.

Dochun♡ Dochun♡ Dochun♡ Dochun♡

“Ohhhh♡ Onii-hyan’s♡ big cock♡ crushing me♡♡♡”

“Nao… my sister’s mine! Haa! Haa! Haaa!”

Each “Onii-chan” fills me with electrifying joy.

“Aaa, feels good♡ I’ll never forget this…♡”

“Nao! So cute! Be mine!!”

“I’m… already yours…♡♡♡ Ah♡ Ah♡ Aaa♡”

I pound her pussy with bed-breaking force, delivering the final blow.

Dochu♡ Dochu♡ Dochu♡ Dochu♡ — Dochun!!

“Ohh♡ I’m breaking♡ I’m gonna break♡”

“Break, Nao! Think only of me!”

“Love you♡ Onii-hyan, I love you♡”

My brain boils, rationality gone.

Zudon♡

“Ohhhh♡ Something huge’s coming! Oaaa~~~♡ ~~~♡♡”

She hits a true orgasm, eyes nearly rolling back, body convulsing. Her pussy writhes, clamping my cock, milking my semen.

“Gu! Such tightness… I’m gonna… cum!”

“Cum… give me your baby, Onii-chan♡”

“Uah! No, Nao, no babies!”

Reality snaps back, cooling me down. Even the morning-after pill isn’t foolproof. I can’t impregnate an eighth-grader.

With my last strength, I pull out at the moment of ejaculation.

Byuru♡ Byururu♡ Byuku♡ Byurururu♡

My cock sprays thick white desire onto her beautiful stomach. The dense, milky semen would’ve surely gotten her pregnant inside.

“Aa♡ Nn… You could’ve cum inside♪”

“Kuu… Still coming…”

“So much, Onii-chan… felt that good?”

Honestly, it was so good my hips nearly gave out. I haven’t been this aroused since sex with my real sister, Ai.

“You’re so cute, Nao…”

“Onii-hyan… don’t look♡ My face is weird, right…?”

“Your dreamy face… so cute. Show me more.”

Seeing a sister happy is my bliss.

(Sisters are so cute… especially a beauty like Nao.)

I know she’s not really my sister, but fucking a gorgeous girl calling me “Onii-chan” drove me crazy.

※

<Ayaka’s Perspective>

(What’s wrong with me…?)

A strange, floating sensation.

(A dream?)

I think it’s a lucid dream.

‘Hey, don’t show me that ugly body.’

That man appears, hurling insults.

(Stop…)

‘Why’d I have to marry such an ugly woman… If you weren’t a Saionji, I’d have refused.’

(Stop… stop…)

‘Good for you, getting rid of that shameful fat lump. Ha… haha!!’

(Stop… stop… STOP!!)

I don’t want to lose my breasts. I’d rather die than lose my womanhood—

Thinking this, I touch my chest. But—

“Huh? M-My breasts… gone…”

My hand finds only empty space where my breasts should be.

…

“KYAAAA!!”

I wake screaming from terror.

“Haa, haa, haa… That was…”

I check my breasts.

“They’re here… thank goodness… a dream.”

A nightmare, the worst kind.

“Milady, are you alright?”

“Oh, Miyabi… Sorry, just a bad dream.”

“I see. If you’re unwell, shall I tell the chef to delay breakfast?”

“Yes… please do.”

“Understood. Excuse me.”

Miyabi Amakawa, my head maid since childhood, responds calmly and leaves. Her presence calms me.

(Phew… my breasts are safe.)

Recalling the horrifying nightmare, I shiver.

(I can’t dwell on this. Think of something nice.)

Nice things. Nice people… a nice man. That man who stole my heart—kind, cool, strong.

The moment I think of him, my pussy leaks warm liquid, jun♡.

“Aa♡ No… so indecent in the morning…♡”

Kuchu♡ — Kuchu♡ Kuchukuchukuchu♡

“Haan♡ My hands… won’t stop…♡”

Memories of sex with him flood my mind, sending sweet tingles from my pussy.

Kuchu♡ Kuchukuchukuchu♡

“Nnn…♡ I want to see sensei soon♡”

My hands move faster, and then—

“Ah♡ — Haaa~~~n♡♡♡”

I climax.

(The ‘coming’ he taught me…)

“So good…♡”

I knead my swollen breasts.

“Not the same as when sensei does it…”

His hands are special, making my blood boil when he touches me.

“Now, my breasts are my pride…♪”

Praised and sucked endlessly, they gave me confidence as a woman desired by a man.

(I want to see him… but no appointments today…)

“Why not invite him to the mansion?”

It feels like a great idea. That man mentioned separation and left the mansion.

But—

“This mansion might disappoint him…”

It’s one of the smaller Saionji properties, with only ten staff. I’m not sure it’d satisfy a guest.

“With Miyabi, it’ll be fine…”

She’s a perfect maid; satisfying guests is effortless for her. So, no time to waste.

“I’ll consult Miyabi♪”

The nightmare forgotten, my heart bubbles with excitement. Then, a tokun in my belly.

I already know what it is.

“This little one wants to see you too, sensei♡”

I murmur, gently rubbing my lower abdomen.