My Little Sister Is the Best F*p Material - Volume 9 Chapter 08: The Naughty Side of My Sister and My Classmate

Volume 9 Chapter 08: The Naughty Side of My Sister and My Classmate

I had to tell Miyu about the school trip. But with her in full-on “I love Onii-chan” mode, revealing I’d be away for four days could complicate things, so timing was critical. Her newfound love for sex was thrilling, but at this ejaculation pace, I’d seriously die. Fixing her broken libido was essential, and with only a week until the trip, waiting until the last minute was out of the question. I had to convince her in the next few days.

In times like these, I rely on a shift in perspective. When I sit down and think hard, my IQ feels like it’s near 200. If Miyu endlessly craves sex, why not lean into it?

We’ve done plenty of naughty things already. Since the day she first drank my cum, we’ve probably had more kinky days than not. But back then, she was just reluctantly indulging my desires. Now, in her lovey-dovey state, she’d likely embrace perverse sex actively. If I push her to the point of shame, there’s room to wedge in some control.

So, after school, I went to her room. Mornings leave me defenseless against her semen-draining, so fun sex is better when I’m still energetic after school.

“We should think about preventing monotony,” I said.

“Monotony? Could that even happen?” Miyu replied.

We stood before her closet, filled with cosplay outfits. Our sex could never get stale, but for me, wanting to try various plays, this was the perfect excuse.

“Better to be thorough, right?”

“Hehe, if Onii-chan wants it, I’m fine with it.”

Even unexpected requests make her happy now. Her love for reluctantly indulging my desires hasn’t changed, even in dere mode. They say being desired stabilizes a woman’s mind, and for Miyu—who’d probably cling to my arm with her breasts if we were apart for a second—this was a delightful proposal.

Still, I hesitated to use her lolita cosplay for sex. Cheap outfits made for our sex are fine, but staining her cherished dresses with my cum feels wrong. If she fully regained her rationality and still allowed lolita sex, I’d go all out. Missing this chance might mean never doing it, which feels like a waste, but we needed something safe for sex.

“By the way, didn’t you get cat ears or something from helping Haruka with her work?”

“Why would I take something only usable for sex with you?” she muttered, rummaging through the closet.

It’s not that her rational side is gone—it’s inconvenient now, sealed deep in her mind out of fear. I know my sister better than anyone.

For Miyu, who loves masturbating in her lolita cosplay, cat ears—something she explicitly said didn’t suit her—wouldn’t be accepted, even for free. If she did take them, it’d mean she anticipated cosplay sex before her libido exploded.

“Oh, found them.”

I had a hunch.

She pulled out cat ears, along with the fluffy panties and bra from under her lolita outfit. What’s that heart-shaped hole in the bra’s cleavage for? Paizuri, maybe?

“Will these work?”

“If you wear them and have sex with me, yeah.”

“Well…”

That’s the idea, but regular sex would be no different from usual. Since she now has sex in her uniform right after school, just cosplaying for sex isn’t enough.

“If I ask, you’d do any kind of play, right?”

“Of course. I’m your sister.”

She put on the cat ear headband, looking excited. How long could she keep this energy?

“I want to watch you change in front of me.”

“Knew you’d say that. If you want, fine.”

She unbuttoned her blouse carefully, stripping. The old Miyu would never have allowed this, so it’s thrilling. Not heart-pounding, but still—my sister changing in front of me. I had to savor it.

The cat tail panties had a small dildo inside, requiring insertion to wear. After removing her bra, she realized this and started pulling down her panties. I stopped her. I wanted to enjoy her naked body in broad daylight. Dere Miyu doesn’t mind me licking her pussy, but what about being fully nude and observed?

“Hehe, what’s up, Onii-chan?”

Her black long hair contrasted her flawless, daifuku-like breasts, glowing. Her smooth, tight pussy was always a work of art. The cat ear headband added an alien charm to her perfect loli cuteness. Seeing her pale pussy, rarely exposed to light, was an unprecedented privilege.

“You love this stuff.”

Despite being stripped and watched in a bright room, she seemed happy. She even spread her thighs invitingly, showing the glistening liquid leaking from her slit. While resistant to exposure, her confidence in her body made her bold now.

So erotic. Yet, I wasn’t fully aroused. I didn’t want to be mean, but her lack of shame made it hard to get excited. I love when she forcibly gets me hard, which is why she drains me daily.

“Can you put on the socks first?”

Naked, she’d normally start with panties or bra. Choosing socks was a quirky touch. I’d seen such erotic images but never the process.

“You’re such a pervert, Onii-chan.”

“Probably everyone likes it.”

I got hard watching my naked sister in knee-highs. I knew it was perverse, but not niche. Naked shirt, naked apron, naked knee-highs—all different, all great.

Her straddling motion while putting on socks highlighted her pussy, the shifting folds like a clamshell exuding odd eros. Like her first cunnilingus, clothing with only her pussy exposed was striking.

Adding paw gloves completed the set, creating a perfectly naughty cat-cosplay sister. Ready to fuck, I exposed myself, then noticed a fatal issue.

The tail dildo blocked sex. Haruka, without a cock, didn’t design it for male sex.

“Then, a blowjob?”

“Yes, as you command.”

Sitting on the bed, she held my cock with her paws, licking the tip. Her happy expression, cheeks softening while sucking, would normally excite me, but for cat-ear cosplay, it felt lacking. I wanted her scornful glare or for her to get so wild she’d be embarrassed.

“Ugh… it feels good, but… isn’t this just our usual sex…?”

“Hm, true. Switch to paizuri?”

She emphasized the bra’s cleavage hole. Dirtying my cute cosplay sister would be thrilling, but I couldn’t lose sight of the goal. Play she wasn’t shy about was meaningless. Even if skipping paizuri was rude, she needed to reach a higher stage.

“Could you… meow and lick me seductively?”

“Huh? What?”

Even she didn’t get it.

“Like, do a blowjob while meowing like a cat.”

“Eh… okay…”

Her face twitched, despite her love for me. Her core personality hadn’t changed—shame could still be triggered.

“Um… nya, nyann… nyannya!”

She meowed, then sucked my cock again. It wasn’t right, but I couldn’t explain how. Even I was embarrassed ordering it. This made today’s sex meaningful.

“C’mon, with the energy you had stripping.”

“Nya, nyaa…! I love licking Onii-chan’s… nyann…”

Hiding half her face with paws, she spoke with zero eroticism. It was the first time I saw her fake a smile so blatantly. Her honest nature doesn’t fake emotions.

I asked her to be happier licking her favorite “Onii-chan stick,” but only awkward silence followed her forced cheer. Her indifferent nature was sad. Would creampies have gotten the same reaction?

“Can’t we just have sex with me in this cat outfit…?”

Miyu pleaded with a troubled look, her brows furrowed. Being stared at with those moist eyes by my sister in an erotic cat outfit, barely more than lingerie, sent a thrill through me like never before. She must be desperate to have sex with me.

“Today, I’m in the mood to cum with a different kind of play. I want to expand the range of sex we can have, Miyu. Maybe something like SM play.”

“U-uh… If it’s Onii-chan’s request, I want to do anything for you… but I don’t know how…”

She was right—it was hard to picture. Role-playing cosplay, candle torture, verbal abuse, spanking—none of it felt like something I could enjoy with Miyu. I’ve never even jerked off to that kind of material. It might’ve been impossible even with someone else.

The times I went full dom with her were driven by runaway lust, not planned special play. Restraint might be doable, but it didn’t feel much different from cosplay.

“Your sister’s dressed like this, so isn’t there a way for Onii-chan to play however he wants?”

Miyu, offering herself as a plaything, wiggled the tail plugged into her, enticing me. Normally, she’d be right—not touching the tail in this cat-ear outfit would be absurd.

But that was also her escape. If pushed too far, her mind would blank out with sex, leaving her at my mercy. If it came to that, I’d rather just fuck her normally.

“The bra and tail are starting to feel like they’re in the way. Let’s take them off.”

“Just so you know, being naked with just accessories is embarrassing!”

“I thought it might make you so desperate you’d act more cat-like.”

“You’re really in that mood today…”

Despite her complaints, she stripped. Her large breasts with pink nipples were irresistible to a breast lover. Above her pure white socks, her plump, obscene labia were exposed, and the cat ears on her head made her naked body exponentially more lascivious.

“To strip me so fast during cosplay sex…”

“I get it, I get it, but please make me cum quick. I’m so horny.”

“Okay…”

Miyu, in her utterly indecent outfit, tried to entice me by pressing her chest forward or meowing to make me cum. But something didn’t click. Her efforts to milk me were pleasurable enough to cum from, but this was supposed to lead to the school trip talk. Wasting semen here without that connection was pointless, I reconsidered.

“At this rate, I can’t do sex today.”

“Ehh?! Even when you’re this hard, Onii-chan?”

She pinched and rubbed my rock-hard cock. It was tough for me too. No matter how much I’d cum that morning, an erection made me want to release. But I hoped a day without sex might cool her down.

“I can’t stand not having Onii-chan’s semen inside me… Throat, pussy, anywhere, just put it in me…”

“You can say that so casually but can’t meow?”

“Anyone would freeze up doing that. Even Kanade-san would find it impossible.”

“Maybe. Yeah, maybe.”

She’s always thinking about sex, but among my acquaintances, she’s second only to Sachiko in common sense. Asking her to meow or do SM play might make her recoil. She’d likely end up like Miyu—trying but failing to get into it, which would be grim.

“Hm… then… tomorrow, ask Kanade-san to try.”

Miyu’s suggestion was loaded. It was surprising—despite her tolerance for my physical closeness with Yamamoto-san, I never thought her runaway libido would let another woman take her place in sex with me. Of course, this wasn’t about outsourcing my needs. If it didn’t work with Yamamoto-san, it’d be my fault for pushing an impossible request, forcing me to follow Miyu’s lead.

Thanks to that, I went to school the next day without being milked at dawn for the first time in a while. The constant emergency semen production had left me with a surplus after a night’s rest. The real challenge was catching Yamamoto-san—she often vanished after school, possibly too busy for sex.

“Hey, Sotomichi-kun. Your complexion’s a bit better.”

Surprisingly, she approached me at lunch. Had Miyu contacted her?

“Barely. What’s up? Did Miyu say something?”

“Nope. Just felt like it was time to talk.”

An esper, huh?

“You looked half-dead until yesterday, then suddenly perked up and kept glancing at me, so I figured something was up.”

Right, she’s sensitive to gazes. The first time we talked at school, she noticed I stopped looking at her, unlike other guys, which piqued her interest. Her confidence that every straight man sees her sexually is what makes her her.

“After school, if possible, could we be alone? Got time?”

“Sounds like a super naughty invite. Can I expect that?”

We spoke in hushed tones to avoid eavesdropping. When I nodded, her face lit up.

“Then let’s do it in the usual reference room.”

She could make time, so after school, we met in the secret reference room. It’s not ideal for illicit rendezvous—only her uncanny hearing made it viable. If students cleared out fast, a classroom would do.

“So, what kind of sex are we doing?”

“Cat-ear costume, meowing while giving a blowjob.”

“That’s bold.”

I showed her the cat cosplay from my bag, borrowed from Miyu, and asked about SM play too.

“Why the sudden kinky fetish awakening?”

“Yeah… fair point…”

Being called a pervert by her was something. Maybe this was overkill for a cure. I explained the situation, stressing its necessity. She wasn’t too surprised, aware of my abnormal sex life with Miyu, and agreed to help fully.

“But, Sotomichi-kun, you carried that naughty outfit in your bag all day?”

“I came prepared.”

“Fair, but you didn’t think I could wear it, did you?”

Taking the cat-ear headband, she held up the dildo-panties and paizuri-hole bra, questioning. I’d overlooked something critical.

“My butt and boobs are way bigger than Miyu-chan’s.”

“Right, no way it’d fit.”

Despite similar proportions, her 20cm height difference meant a 600ml breast volume gap. Her boobs are huge.

“So, I’ll just wear the cat ears.”

“Can you do it?”

“Of course. Miyu-chan just lacked motivation.”

She propped her phone against the wall, calling Miyu via a messaging app. No hesitation, huh?

[“I didn’t expect a call.”]

“Wanted Miyu-chan to learn from this.”

[“Even if Kanade-san’s great at it, I won’t copy.”]

Yamamoto-san unbuttoned her blouse while talking, her panties already on the floor. She had no qualms exposing herself at school. Her stripper-like seductive undressing was fine, but her casual approach to sex thrilled me more.

“Miyu-chan, watch. Sotomichi-kun’s already hard, right?”

“Y-yeah…”

My pants were forcibly lowered, ready for sex before the mood even set. She pulled her bra up to expose her nipples and tucked her skirt to show her pussy. It’s subjective if that’s erotic, but her no-nonsense approach to sexy prep gave me a solid thrill.

“I’ll remind you both what’s important.”

She licked my cock. Without waiting a second for my move, her aura shifted. Her direct gaze and slack mouth felt like a sex slave pledging loyalty, as if she truly saw herself as my slave.

“Today, Sotomichi-kun is my master, nyann~.”

Instead of her usual long licks, she used gentle, precise flicks, savoring every part of my cock. She sucked the glans with each precum leak, relished the taste, and kissed the frenulum, focusing purely on making my cock feel good.

“Nn, haa… Master’s so delicious… I’ll serve lots, so give me a reward, nyaa… lick… chumu… lerolero, nchu…”

“Ugh, kuh… haa… if you do it that eagerly…”

I was getting into it. No time to prepare, yet her licking the salty pre-wash urine excitedly made me want her to taste more of my lewdness. Rubbing her nipples on my knees, wagging her hips as if a tail were there, she expressed joy.

“Hehe, don’t twitch, Master~ Cats can’t resist moving things… hamu…!”

She pounced, engulfing my cock, using long strokes from lips to throat. Like a cat devouring food, her fierce blowjob made vulgar jubo jubo sounds, loud enough for the hallway.

“Ugh, ah, aah… s-so good…!”

I could cum even with her. Holding back was unbearable, toes curling.

“What happens if I scratch Master’s naughty body, nyaa~?”

Her hands reached up, clawing my nipples through my shirt. The soft tongue on my glans contrasted with the sharp nipple teasing, a perfect spice in waves. What started as milking turned into her enjoying making me moan.

“Uku… aah…! C-cumming… ugh…!!”

The dam broke, unloading a ton of cum into her mouth. Despite my thinned semen from yesterday’s overload, she swallowed it all unfazed.

“Heh, still tastes awful.”

A compliment from her, said with a beaming smile. I felt slight regret but also rare satisfaction, unable to react.

“Next, SM play?”

“So soon?!”

“You’re still rock-hard.”

My cock was still erect. Sadly, I had energy to spare. The break helped, but her eroticism fueled my recovery.

Yamamoto-san turned around, raising her hips so high her dripping labia were fully exposed, rubbing against me. Incredibly erotic. Her thick, meaty buttocks were stunning.

“Hey, Master… please punish this filthy pig who craves another man’s rod…”

She switched the mood instantly, inviting my dominance. My cock hardened to the point of straining. I wanted to grab her ass, growl “You filthy sow!” and thrust into her.

The overwhelming arousal looped me back to calm, a bead of sweat trickling down. To think a woman could immerse me in such play. I couldn’t deny her claim that Miyu just lacked motivation. This was a success for my plan—tonight, I’d use this to push my desires on Miyu while subtly mentioning the school trip.

“Ah… M-Miyu, are you still watching!?”

I’d forgotten she was on the call during my ejaculation. She suggested this, but was it okay?

[“I’ll thank Kanade-san later, so Onii-chan, come home immediately. We have something important to discuss.”]

“Uh? Oh, okay…”

Her voice was flat, not angry—closer to her rational tone. Maybe she really had something serious. But what about my half-cocked lust?

[“Etiquette says Kanade-san should handle it, but this is urgent. I’ll apologize for you, so wrap it up.”]

“Got it. …Yamamoto-san, is that okay?”

“Hehe, of course.”

She stood, redressing with a look expecting an apology later. Having made me cum once, she seemed satisfied. The call with Miyu had ended, and her tone suggested her rationality was back. I had to hurry home.

“…By the way, Yamamoto-san, you mentioned reminding us of something important. Is that what Miyu meant?”

“Maybe? I just wanted to say some things are better unchanged.”

She meant before I got used to women. Following girls’ lead without a shred of manliness suited my relationships best. She liked me being at her mercy during sex. Honestly, it felt like her preference, but I’d keep it in mind.

After fixing her uniform, she left quickly. She’d made time despite her busy schedule. I should’ve asked what she was up to.

At home, I bathed as Miyu instructed, then went to her room. She sat with hands on knees, her demeanor confirming her rationality’s return.

“So… the important talk?”

I probed, gauging her.

“It’s like a switch in the back of my brain flipped off. Not a clear feeling, but it’s perfectly in place.”

“And that brought you back?”

“Yeah.”

Her movements were stiff, as if balancing a bucket on her head, minimizing external stimuli. Temporary, then.

“What triggered it?”

“Hm. Kanade-san’s depraved masochism snapped me out of it.”

“Figured.”

Her eroticism was unreal. Is there any play she can’t do? She might even develop my ass if I asked.

“So, the important talk is I want to solidify this feeling. For the future.”

She wanted to stay herself even during sex with me. Despite being swallowed or creampied, she refused to let her instinct to crave my seed override her, especially avoiding baby-making frenzy mode. I agreed.

“What about the lust-driven Miyu?”

“Hm, like how people debate if someone’s true self shows when sober or drunk?”

“Yeah, where their raw self comes out.”

“But I think a person’s personality includes their cultivated rationality. When drunk, something’s missing from their true self.”

It made sense. Humans act within a mix of innate instincts and acquired rationality, choosing amid conflicting thoughts. Losing control makes you act like another person, but that’s not a changed personality or true self revealed.

Miyu’s strong rationality, lingering lolita-loving nature, and illicit desire for me all make her her. Her rationality collapsing from creampies isn’t her true self—it’s a balance issue. The instinctive Miyu is part of her, but her core is the cold, stoic one, acknowledged through our intense months.

“So, I want to train my brain not to succumb to lust.”

“How?”

“Stay completely unresponsive until you creampie me.”

“Huh…”

Never tried that. Calling sex brain training is uniquely her.

“Like a challenge to endure, but I cooperate, right? Like doing it quietly?”

“Yeah. It might be boring sex for you, but just enough to cum.”

“Got it.”

“…Why are you already hard?”

“No idea.”

It wasn’t just Yamamoto-san’s unfinished job. Her play idea excited me.

“Let’s get it over with.”

“Yep.”

We stood, stripping. No complaints if I didn’t ogle. Like a duty, we shed all clothes, dropping them to the floor, and got into missionary on the bed.

Miyu, in unresponsive mode, was silent. Could sex even start like this? Checking her pussy for wetness, I found it soaked as if we’d done foreplay. I was rock-hard. Why are we siblings like this?

Silently, I entered her. Normally, she’d sigh, but she stayed stone-faced, showing no pleasure. As if unaware of my cock, she just swayed with my thrusts.

My cock felt her vaginal walls clearly, pleasing me and supposedly her. Yet, her expressionless face waited only for the end. Even avoiding weak stimulation or hitting her sensitive spots, she didn’t flinch.

Sex is like marking her as mine, claiming reproductive rights. But her unresponsiveness made me pathetic. My thrusting turned into a virgin-like flopping. Her body relaxed, and while I pistoned desperately, she just blinked at me. Maybe my sex wasn’t good.

“Haa… haa… haa…”

Yet, my heart pounded with wild joy. Unprecedented mental ecstasy. My cock felt bigger inside her.

I was the only one excited, feeling good, lusting after her body. She entrusted herself to me, offering her precious hole. I was the one begging for sex. My true self—a brother who can only cum with his sister—resurfaced. The silence made me hyper-aware she’s my sister, thickening my semen, weighing my balls. I reverted to the pathetic me, reliant on her for release.

“Miyu… sorry, I’m gonna cum…”

“Can’t hold out a bit more?”

Her disappointed, cold voice. I couldn’t hold back.

“Can I cum inside?”

“Well, sure. Go ahead.”

Her businesslike permission was the final push.

“Ugh…”

“Whoa, wait… it’s so thick. You came once already, right?”

“Sorry, my lust’s insane.”

It wasn’t just my body. Unresponsive Miyu was too erotic. I love her. So much.

“Hey, Onii-chan. You get it, right?”

“I know in my head. But I love you, Miyu.”

“That’s what bad guys say… ah, wait… nn…!”

Post-ejaculation, my thickened cock went straight into round two. She tried staying unresponsive despite her limit, falling silent again, expressionless. But I saw her gripping the sheets tightly.

The earlier ecstasy was gone. Now, I was mating with her, driven by the urge to fill her womb. It was love. Her unresponsiveness didn’t matter—I followed my instincts, coupling with my sister.

“Miyu… Miyu…!!”

I couldn’t stop. I ravaged her, focused only on cumming, thrusting for the pleasure of her vagina. Touching her raw pussy filled me with joy, love, and lust overflowing.

I think I fucked her longer than I realized. I vaguely heard her scream, “Onii-chan, I can’t…!!” maybe on the fifth cry. Her hands pushed my head, but I sped up for the finish.

“Miyu… ugh… haa, ah… cumming, cumming…!!”

Byuru byururu, byugu, byurururu, byuu—!!

I unleashed my most forceful ejaculation in days into her deepest parts. Relishing the joy of cumming in my sister’s vagina, my balls emptied endlessly.

“Haa… haa…”

Panting, I looked down at Miyu, eyes rolled back. I’d messed up. She’d be a succubus by tomorrow. And I forgot the school trip talk.

But today made me rethink. I thought I had to control her lust, but that’d ruin her. Her willpower strengthens with responsibility. So, I won’t hold back for her sake anymore—I’ll let her handle my uncontrollable lust. That’s our sibling dynamic. Needless to say, from that night until the school trip morning, she drained me relentlessly, no sleep spared.

T/N; Aayayaayyaya, so basically this is the end of volume 9. I have no access yet to volume 10, if anybody has one, then you can add me on discord, @arrochi, then send it to me there. Besides that, I plan on doing the oneshot light novel with illustrations of the author, this same novel but more of a oneshot fulfillment-fantasy novel, where they have sex early and stuffs. Expect it around next week as I will be taking a break for a while.