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

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Chapter 5

I ended up going shopping with Misa-san, the number two at the high-class escort agency, while my sister Ai was at summer cram school for her high school entrance exams.

“Hmm, let’s hit the salon first?”

“Uh, I didn’t make a reservation…”

“No worries, I’ve got my go-to place.”

At the salon, I got a trendy haircut, then Misa-san took me to a casual brand store in the shopping district to buy clothes.

“Yup, looking good~ You’re so hot now, any girl would turn her head♪”

“That’s a bit much…”

I’ve been more active lately, so my physique’s improved, but I didn’t think a haircut and new clothes would change that much.

“I’m serious! You’ve got great raw material.”

“Uh, thanks.”

Misa-san clung to my arm, whispering in my ear. Her soft breasts pressed against me, munyu, the sensation stirring my lust. Her sweet mix of feminine scent and perfume invaded my nose, fueling my desire.

Sensing the heat swirling in my groin, Misa-san said—

“—Wanna take a break? I know a great spot♪”

She led me toward a flashy hotel.

“Wait, isn’t this… a love hotel?”

“Yup, best place to rest, right? And… your friend down there’s at its limit, isn’t it?♡”

She rubbed my crotch, surisuri, teasingly.

“Hau…! I can’t walk if you do that!”

“Fufu, you’re already rock-hard♪ Don’t rip those new clothes.”

Joking, she teased the tip of my tented pants with lewd fingers.

“Let’s… get inside quick…!”

“Right♪”

Unable to resist my urges, I practically dragged her into the hotel.

For the rest of summer break, I kept secretly hooking up with Satsuki-chan and other women behind Ai’s back.

…

In the dim pink lighting, a man and woman clashed their bodies fiercely.

“Kuh! I’m gonna come again!”

“Nhaa♡ Go ahead, shoot it deep inside…!”

On the bed, the man pounded his massive cock—already slick from multiple loads—into her dripping pussy from behind.

Paan♡ Paan♡ Paan♡ Paan♡ Dochun♡

“Nnun~~~♡ Coming, coming~~~♡♡♡”

The woman arched her back, drowning in pleasure, trembling in climax. The man, spent from his release, collapsed onto her back.

“Ahn♪ You’re heavy!”

“S-Sorry, it felt too good…”

“Fufu, kidding♪ You’ve really gotten good at this.”

They weren’t lovers, but they’d shared their bodies many times.

“Maybe it’s time to graduate…”

“Graduate… I…”

The man fell silent, unsure what to say. The woman hid a sad expression, staying quiet too. After a moment, the man, as if resolved, started thrusting again.

“Ahn♡ So insatiable♪ Fine, ravish me as much as you want.”

Hearing her, he growled like a beast, shifting to rough mating.

“Ah, no♡ Too intense! You’ll break me!”

Pinned down with ferocious strength, she was ravaged by the beastly man. The bed creaked like it might break, her womb battered by his monstrous cock, gotsun.

“Ow, that hurts! I didn’t teach you such rough sex…”

She cried out in pain, thinking to stop—when he gripped her full breasts, squeezing hard.

“Hiii♡ My oppai are gonna burst… ohhh♡♡♡”

Lightning pleasure shot from her breasts, searing her spine and brain.

“Ohhh♡ Ahhh♡ No… that’s… ohhh♡♡♡”

Her pussy was pounded, gotsungotsun♡, her breast nerves teased, guniguni. Despite the near-rape intensity, her body reveled in it.

(I don’t know this feeling…♡ Ravish me more♡)

Her voice melted into a sultry moan…

Dochun♡ Dochun♡ Dochun♡ Dochun♡

“Yiii♡ That’s good… harder, ravish me more♡♡♡”

Begging for more, she shook her peach-like ass, demanding to be taken.

“Graduate… you sure?”

“No! No graduating… ravish me more♡♡♡”

Drooling, she wiggled her hips, screaming for more.

“Then don’t say it again, okay?”

He spanked her jiggling ass, bachi! Bachi! Bachi!

“Auu! Sorry, I won’t say it again♡”

“Good. Let’s stay friends, Misa-san.”

He gently rubbed her reddened ass.

After that, he fucked her until she passed out, only stopping when his balls were empty, regaining his senses.

This was two days before summer break ended.

Ai’s Perspective

On the last day of summer break, I went to Onii’s room in the morning.

“Onii, you awake?”

“Nn… let me sleep more…”

He looked exhausted, refusing to get up. He used to jump up to pounce on my body…

“Hey, I need to talk, so get up!”

I yanked off his blanket, revealing a towering bulge in his pants, like the Eiffel Tower.

(Wow… it’s definitely bigger than before. Onii’s changing so much…)

My pussy wettened, jun♡, as I stared. Noticing, he sat up and pulled me close.

“Let’s do it once, Ai.”

“Wait… I said we need to talk… haaan♡”

He kneaded my breasts, kunikuni♡, and stripped me in seconds as I squirmed in pleasure.

“Here I go.”

“No, we need to… ah!”

His massive cock plunged in, zubo♡, with fierce momentum.

“Uhaa… your raw pussy’s the best, Ai.”

“Hau♡ Onii… your cock’s too big…”

It’s definitely bigger, the flared head scraping my insides, making my legs weak. As I collapsed, he flipped me onto all fours.

Pachun♡ Pachun♡ Pachun♡ Pachun♡

“Ah, ahhh~~~♡ Onii’s hitting my good spot…”

“Here, right? Take it!”

He targeted my sweet spot near my womb like he knew my body perfectly. His rhythmic, multi-angled thrusts made my hips tremble, buruburu.

“Oh, gonna come, Ai? I’ll speed up.”

Pachu♡ Pachu♡ Pachu♡ Pachu♡ Pachun♡

“Auh, ahhh♪ Coming! Coming, coming~~~♡ Haaa…♡”

Pounded by his thick cock, I climaxed easily. In sync, he pressed the tip deep, dochun♡, shooting hot cum.

(He’s pressing my womb… I’d be pregnant for sure without the pill.)

Dazed, I glanced back—he looked like he could go again, full of energy.

(His body’s so muscular now… he doesn’t even do sports…)

“Haaa… creampying your pussy is the best, Ai.”

The guy who gave me those shady pills praised my pussy, like he was comparing it to others.

My suspicions turned to certainty.

“Hey, Onii…”

“Hm? What, Ai?”

“You’re… cheating, aren’t you?”

I felt his cock wilt inside me.

“W-Why would you say that…?”

“I can tell… I’ve been watching you…”

The signs were endless—his new haircut, stylish clothes, better sex skills, and buff physique. He’s a different person from a month ago.

And the clincher…

“You smell like another woman…”

“Huh!?”

He sniffed himself, practically confessing.

“Who is it?”

“Uh, well… um…”

“Is it… Satsuki-chan?”

“Ugh… how’d you know?”

I knew it. When he first met her, he was smitten. He might not have realized, but I saw it from the sidelines.

“I’m calling Satsuki-chan.”

“Calling her… here?”

“Yup.”

I grabbed my phone and called her. When I said I needed to talk, she agreed to come over without hesitation.

(What is she gonna do after exposing our affair…?)

I’d never heard of a friend stealing your brother. I couldn’t tell if my forbidden love or her possible normal relationship was right.

…

(AI POV)

“Hey, Ai!”

“Oh, Satsuki-chan…”

She showed up, acting totally normal, no sign of guilt.

“Morning, Onii-san♪”

“Uh, yeah…”

They greeted each other—way too close! Close enough to kiss, making me panic.

“Satsuki-chan! You know why I called you, right?”

“Huh? Hmm… maybe Onii-san missed me?”

She’s definitely playing dumb. Maybe she doesn’t care if the affair’s exposed.

“You’re… cheating with Onii, aren’t you?”

“Cheating? Why would you say that, Ai?”

“B-Because… you’re doing naughty stuff with him, right?”

“Yeah, we’re having sex, but what’s that got to do with you?”

(He didn’t tell her about us? Right, he can’t admit to incest with his sister…)

Onii, who’d been frozen, spoke up.

“Sorry, Satsuki-chan… the girl I’m dating is Ai…”

“Oh, really? Knew it♪”

“Knew it!?”

“Not really, but—”

Looking at me, Satsuki-chan said—

“Only someone as cute as Ai could outshine me.”

She said it with an infuriatingly adorable face.

…

My classmate Satsuki-chan’s always been a carefree girl. I get along with everyone, but her vibe clicked with me. But—

“Why, Satsuki-chan…? If you knew, why…?”

“Why? ‘Cause I fell for him too, duh.”

Duh? You steal another girl’s guy just like that?

“That’s not right…”

“Not right? Who’s more wrong, me or you, Ai?”

I was speechless. I know sleeping with my brother isn’t normal.

“You’re super popular, right, Ai?”

Sure, tons of guys confess to me. I hate to say it, but… I’m probably cute.

“Smart, athletic, cute face, great personality. And big oppai.”

Her mention of my oppai made me blush. Is that how everyone sees me?

“I’m dumb, bad at sports, used to be flat-chested… I had nothing on you.”

Satsuki-chan’s monologue continued.

“But… I got bigger oppai and some confidence. Now I can accept everything about Onii-san.”

She looked so mature.

“Even if he screws tons of other women♪”

The room froze at her bombshell.

Onii’s face went pale.

“You can’t forgive him, Ai?”

“No way I could…”

“I can. As long as he loves me, I don’t care who he sleeps with. So let’s make him choose—me or you.”

I can’t win.

I’m kicking up a fuss about cheating when we can’t even marry, while Satsuki-chan’s all mature, letting him cheat. She praised me, but our positions are reversed. Our faces and breast sizes are about equal… but I’m not confident. Her heart’s bigger than mine.

And… she can marry Onii. Date normally, marry, have kids, be happy. For Onii’s happiness, she’s the obvious choice.

(She’s too dazzling for me…)

Crushed by defeat, I’d meant to expose their affair but ended up pathetically on my butt, tears welling up.

(It’s over… Onii, who I’ve always loved, is gone…)

I wished I’d pretended not to know.

※

Two pairs of eyes stared at me.

I’d been frozen, unable to move.

Ai collapsed to the floor, suton.

Satsuki-chan’s words—choose Ai or her—echoed.

I looked at the two girls.

Ai, with her brown hair, big adorable eyes, and that miraculous middle-schooler cuteness, not yet fully mature. A perfect beauty, inside and out, who I’ve always loved.

And then…

Satsuki-chan, with silky blonde hair, blue eyes, a gyaru yet refined beauty. The heart-pounding feeling when we met… it was probably love. My first crush outside Ai. That’s why I was so down when it didn’t work out… I get it now.

Choosing only one is so cruel.

With family love included, it might be Ai. But we can never marry, never be husband and wife.

Satsuki-chan, though—I could marry her, build a happy family, maybe even keep cheating with her blessing. For my lower half, she’s the clear choice.

(Be honest. Get your first love and still enjoy other women… no need to hesitate.)

My head and my dick both screamed Satsuki-chan.

But—

“I… love Ai the most in the world…”

I chose Ai.

The moment I almost picked Satsuki-chan, a childhood memory of Ai flashed in my mind.

“Look, how’s my massage?”

“Nnn… my oppai tips are tingling…”

“You’re so cute, Ai.”

“Huh?”

“When we grow up, I’ll make you my bride!”

Young me promised to marry Ai, even though siblings can’t.

(What face did she make back then…?)

A hazy memory.

I remembered young Ai’s face…

And it overlapped with—

“Onii, I’m… so happy…”

—Ai’s sparkling smile now.

※

“Onii, I love you…♡”

Zuchun♡ Zuchun♡ Zuchun♡ Zuchun♡

In missionary, Ai and I whispered our love, connected.

“I love you too. You’re the cutest girl in the world.”

“Uuu, thrust harder with your cock… love me♡”

I sped up, pounding her pussy, pan♡ pan♡.

“Wow♡ You guys are really doing incest♪”

Satsuki-chan watched, no disgust, maybe even enjoying it.

“Here, Ai? Your portio, by your womb, feels good, right?”

“Ah, ah, there♡ Your cock’s so good…!”

Using tricks I learned from cheating, I made Ai writhe. I’m a scumbag, but I can’t let this girl go. To keep her, I held her tight, attacking her sensitive spots.

“Onii♡ Your cock’s amazing♡ You’re gonna break me…”

“Of course, I’m making my cock rock-hard to break you!”

Dochun♡ Dochun♡ Dochun♡

I pumped blood into my cock, making it as hard as possible.

“It’s swelling more♡ You wanna ravish me that bad?♡”

“Yeah! I’ll make you think of nothing but me!”

Pan! Pan♡ Pan♡ Pan♡ Pan♡

“Ohh! No… I’m going crazy♡”

“Go crazy! Your big brother’ll take care of you!”

“Yiii♡ Ah, ah, ah… I’m flying, Onii… Onii♡ Ohhh~~~♡♡♡”

Ai climaxed with a wild cry. Her voice and expression drove me to slam my cock deep, her pussy squeezing, kyuu♡, begging for my cum.

The taboo thrill made me pour every drop from my balls into her.