My Little Sister Is the Best F*p Material

Volume 8 Chapter 04: Two Girls Who Want to Be Used

The night before my date with Yamamoto-san, I was with Miyu, sitting around a birthday cake.

“Happy birthday, Onii-chan.”

Miyu bowed deeply while seated. Why such formality on a joyous occasion? The reason became clear soon enough.

“Here. It’s a cliché way to give it, but this is your birthday present.”

Miyu handed me a chocolate bar, the kind you’d find for a hundred yen anywhere. This was apparently my gift for my first birthday as her lover.

(So, this means…)

Miyu said it was a “cliché way to give it,” not that the gift itself was cliché. That implied the chocolate bar wasn’t the real present. What could be associated with this rectangular shape? A paper ticket, obviously.

(She said she’d think about it, but to actually prepare it…)

Peeling back the chocolate’s foil, a slip of paper fell out. Picking it up, I read: “A ticket to have Onii-chan’s wish granted once.” In short, Miyu would do anything I asked, just once.

“Just to confirm, this isn’t a ‘listen to me talk’ ticket, right?”

I asked Miyu as she sliced the small whole cake.

“You think your sister would give you such a cheap gift?”

“Of course not.”

Her voice was cool, despite the risqué note on the pink-edged paper. Miyu’s commitment to keeping her word is unmatched. She’d rather give a normal gift than raise false expectations.

“Since it’s my birthday, can I be a little selfish?”

“Selfish? That’s rare for you. Let’s hear it.”

Miyu stabbed her fork into a slice of cake, popping a big piece of sponge into her mouth.

“With a ‘one-wish’ ticket, it’s hard to define what counts as a single wish. Say I make an naughty request, like, ‘I want to watch Miyu masturbate.’”

“Go on.”

Miyu’s face said, What else would you use it for?

“If I get turned on and ask you to get me off, you might not mind since masturbation’s more embarrassing for you. But it could count as a second request, so you could refuse.”

“True.”

Miyu answered calmly.

“So, I’d regret not including that in the original wish. Anticipating that, I’d overthink the first wish.”

“And?”

“What if it’s not one wish, but one day?”

“Hmm.”

Miyu kept eating, focused on the cake—a premium treat from a new shop in town, reserved in advance, with even the strawberries on top being high-end.

“If I use the ticket, you’d grant my wishes until I’m satisfied for that whole day, until midnight. It’s clear, objective, and more fun.”

“If you’ve got any conscience left, I’ll allow it.”

“Great.”

She agreed. Now I could enjoy the cake without worry.

“Then I’ll rewrite this ticket as ‘A day of absolute obedience to Onii-chan’s commands, no matter how bad.’”

“Is your conscience really still there?”

“Of course.”

Miyu, mid-bite, shot me a dark, skeptical look. I might’ve lost some brotherly points, but I couldn’t back down. I’d just realized my duty to savor my sister.

“Anyway, tomorrow, Dad and the others come back, right? So, tonight… how about it?”

Trying to take the lead, I couldn’t hide my awkwardness. How do other guys invite girls to get intimate?

“You’ve got a date with Kanade-san tomorrow, so I wouldn’t recommend it.”

“I know, I usually avoid it before seeing Yamamoto-san. But just for tonight…”

I’ve always refrained from sex with Miyu before dates with Yamamoto-san to save up my desire. Miyu knows male love deepens through lust, so she deliberately holds back to help me create a romantic vibe with Yamamoto-san.

“Well, this time it’s a bit different.”

Miyu continued, her face serious.

“If you don’t rest tonight, you might die.”

She said it softly, without a hint of jest.

“What!?”

“I can’t say why. Just a feeling. Maybe not tomorrow, but another day. If it’s tomorrow, sex tonight might kill you.”

“What’s that supposed to mean?”

I didn’t understand, but her mysterious confidence was enough to make me drop the idea.

“If that’s the case, fine…”

We’ll have plenty of chances for sex later. Missing tonight isn’t a big deal.

“Anyway, thanks for celebrating my birthday. This cake too—it really means a lot.”

“No problem. I’m your sister, after all.”

Miyu finally smiled brightly, and we ate the cake together. I don’t fully grasp the “Onii-chan’s sister” thing, but the vibe comes through, so I let it slide.

“And this ticket. I didn’t think you’d actually give it.”

“Well… just happened.”

Miyu said something cryptic and stood to clear the dishes. She’s extra mysterious tonight.

“Oh, one more thing.”

After washing dishes, she returned.

“What’s up?”

“Something we’ll need going forward.”

She showed me her phone screen—a calendar app. We’d share schedules.

“Definitely a must-have for couples.”

“It’s essential for us.”

Emphasizing it was for us, she had me install the app and linked two calendars. One was “Sibling Schedule.” The other—

“So… naughty…”

“I struggled with this one. But since you’re a year older, I thought it might be okay.”

“Yeah.”

The second calendar, which Miyu was filling out, was titled “Onii-chan’s Sexual Relief Schedule.” For us lustful siblings, knowing when sex is possible is critical. Using a shared app, Miyu ensured stress-free intimacy. It included her menstrual cycle, tracked with precision thanks to her pills.

“Grayed-out days are off-limits? Regular plans are here too.”

“This one’s the main one. The other’s for public use.”

“Got it.”

Gotta be careful not to mix them up.

“So, any white slot means I can…”

“Yes, you can use your sister.”

Miyu said it matter-of-factly. “Use” meant using her body for sex—her mouth or vagina, freely, for my release.

The app’s purpose was to sync schedules without asking. In reality, it was a “sister reservation app” for my ejaculation. A god-tier app?

“Huh, I don’t have edit access. How do I reserve?”

“You’ve got stuff to sort out first, right? This was just a chance to bring it up.”

A premature birthday gift, huh?

“So, this sister reservation feature…”

“Unlocks once you settle things with Yamamoto-san.”

A conditional unlock. Frustrating, with such a lewd app dangling before me.

“Handing me this, you know I’ll use it once it’s active.”

“I installed it knowing you’d use even something this perverse.”

Fine, I’ll live up to that. Once everything’s settled, I’ll fill that calendar. It seems to support hourly slots, so I could use it to summon her when I’m in the mood.

“Tomorrow’s the day, then. I’ll sleep tonight and go all out.”

“Good luck. I’m rooting for you.”

Miyu clenched her fists, giving a cute cheer. With such an adorable sister, I need to become a brother just for her, ASAP.

The last day of summer break arrived. I was meeting Yamamoto-san at the station for an amusement park date. Unlike the one with Yuka, this was a resort-style park, perfect for couples, with fireworks as the main event—the only place left for them.

Waiting by a pillar near the gate, I spotted a dazzling girl approaching. Her earrings gleamed, her short skirt swayed, and her long legs drew every passerby’s gaze. She walked up, gracefully tucking hair behind her ear, her heated eyes locked on me.

“Morning, Sotomichi-kun.”

Even her simple words felt sultry.

It almost felt like she was saying “I love you.”

“Morning. You’re different today.”

“Yeah, how is it?”

Her dreamy eyes dropped shyly, showing off her outfit. A shawl shielded her shoulders, but the lace-trimmed tank top underneath accentuated her curves, making her look more mature.

No matter how stylish, my eyes went to her prominent chest. A guy’s struggle—or maybe a busty girl’s? …No, her breasts look bigger today, and their shape is perfect.

“You noticed? I went all out with the push-up today.”

She’s boosting an already ample chest? That’s just unfair. A feast for my eyes, though.

“I figured you’d like the view, Sotomichi-kun.”

“I’m touched you thought of me first. I also noticed you went to the salon. The earrings suit you.”

Since we’re aiming for a proper couple’s date, I’ve gotta show I’m looking beyond her chest.

“Aw, I’m glad. You really do see me.”

Smiling softly, Yamamoto-san winked invitingly and started walking with a cheerful bounce.

With her standing out so much, anyone would notice. She’d probably beam like that no matter what I complimented. Her straightforward “like” makes her so easy to be around.

I caught up, walking beside her. Her high-end, mature-cute style—mixing sophisticated charm with youthful skin-baring flair—was striking. Her heels, higher than usual, made her slightly taller than me.

“Too much?”

“The heels and earrings?”

“Yeah.”

“Not at all.”

We passed through the gate separately, then rejoined, heading to our platform. As a guy, I get what she’s hinting at. A shorter guy stands out poorly, and as someone who used to only like pure, 2D-style girls, I’m not immune to resisting gal-like accessories. But denying a girl’s preferences outright? Nah.

“If it’s a look you love, that’s what matters.”

It’s a sign of her trust. If I have any redeeming quality, it’s probably this. Whatever our relationship becomes, I want to be someone she feels safe with.

“You’re gonna make me fall for you.”

Aren’t you already?

“Well, I’m here as your boyfriend today. I’ll… try to keep my urges in check.”

Time to man up. Even with Miyu’s abstinence order leaving me pent-up, I won’t lose to Yamamoto-san’s sexy figure.

“Aw, you don’t have to. I love how you can’t help thinking naughty thoughts.”

“Bit of a mixed signal…”

She’s got a point, though. If we were really dating, I’d probably prioritize lust over everything. Gotta rethink that one.

As we descended the station stairs, the train arrival chime rang. We lined up at the back of the platform.

“Hey, Sotomichi-kun.”

The train pulled in, wind catching Yamamoto-san’s hair. She held it with her right hand, smiling seductively.

“I heard you say you’d be my boyfriend for this date.”

It was a step beyond our near-lover friendship—a clear intent to date closer. With Miyu’s nudge and all the times Yamamoto-san could’ve been my girlfriend, this moment felt like the culmination of our journey.

“You can count on me.”

Nothing drastic changes, but I’m aware I need to take responsibility now.

Miyu’s “feeling” last night? Probably spot-on. Yamamoto-san’s vibe confirms it. Something’s happening today.

“Let’s go be all lovey-dovey!”

“Wait, Yamamoto-san, you’re too close…!”

She clung to my arm, pulling me onto the train. Her body’s softness and the stares from others left me flushed, cooled only by the train’s AC.

An hour later, we arrived at the amusement park. Despite summer break ending, the entrance was packed with young people.

“Came early, and it’s already this crowded?”

“They’ve been adding new areas fast lately. It’s been a while, so I’m excited.”

“Really? It’s… my first time.”

The scene overwhelmed me. The grand arch at the entrance, the castle in the distance, attractions peeking through the hills—it was like a TV spectacle brought to life. But more than the park’s design, the crowd stood out. They were nothing like my usual circle.

Groups of students—mixed, all guys, all girls—chattered loudly, dressed in character merch or matching uniforms, soaking in the vibe. Some were filming for social media. And, naturally, tons of couples. Most were the “popular” type—SNS-posting, stylish guys and picture-perfect girls, straight out of the top of the school caste. Not the kind I’d meet at meetups.

This place didn’t welcome loners or those who preferred solitude. For an otaku like me, it was an alien world.

I told Yamamoto-san to expect more, but I’m embarrassingly nervous. I’d probably feel this with Miyu too, so maybe this is my authentic “boyfriend” behavior.

“You okay, Sotomichi-kun?”

Yamamoto-san lifted her bra cups, jiggling her chest. It was like a perfect blend of mochi and pudding.

“Look, look!”

Jiggle, jiggle, jiggle… She kept shaking, her already massive chest enhanced to absurd levels.

Incredible. The smooth, wavy softness of her breasts melted my tension.

How does Yamamoto-san get guys so well?

“Because I care about the person I love.”

Her bright smile and understanding of male feelings make her the ideal girlfriend. It feels nostalgic—our first talk was about her chest too. She’s so casual about letting me touch.

“Once we’re in, where should we start?”

She studied the park map as we neared the gate.

“Your call. I’m more into the bike ride around the water or the street with character statues. Oh, but I want to try the shooting game.”

Yuka and I did it, and gun games are fun.

“Can I pick the area order?”

“Go for it. Appreciate it.”

She’d plan our route, I’d point out shops that caught my eye. With roles set, we waited, then checked in at the entrance.

We got wristbands with IC chips—blue and red pairs. We put them on our linked hands’ wrists, walking straight into the park. Our fingers naturally intertwined, the red and blue bands crossing, creating a couple-like vibe.

“Sotomichi-kun.”

Her clear, heart-melting eyes met mine as she called out. Her unfiltered affection is her greatest charm. It’s easy to overlook with all her qualities, but the longer we’re together, the stronger I feel it.

“What’s up, Yamamoto-san?”

I replied to the tall, graceful girl beside me, her steps elegant in her familiar heels.

“Um, sorry to ask so soon, but… can we grab food before queuing?”

She looked a bit embarrassed.

“I was so excited this morning, I couldn’t eat…”

“No problem, but you were that excited?”

Her almost childish enthusiasm made me grin. Restaurants weren’t open yet, so it’d be souvenir shop snacks or stall food.

“It’s a date with someone I love, after all.”

Her eyes brimmed with feeling, then she smiled and approached a stall.

“One popcorn, please.”

She ordered with a singsong rhythm. The staff, mimicking a movie character from this area’s theme, scooped fresh popcorn with playful flair, filling a bucket.

“Four hundred yen!”

“Here’s the exact amount.”

“Thanks! Have fun!”

The staff’s high energy sent us off. The popcorn, labeled “Italian Salt” to match the area’s theme, tasted distinct from regular salt. I tried some.

“Mmm, yummy!”

Yamamoto-san hugged the bucket, queuing for an attraction. Despite her polished look, she kept her youthful charm. No one matches her ease. Being with her is pure happiness. I love that about her—a feeling rivaling romance. And now, I’m not afraid to admit it.

“I’ve got a favor to ask, Yamamoto-san. Is that okay?”

“What, what? Anything, just say it!”

Her eyes sparkled with anticipation. Her pure reaction made this hard to say, but…

“I said I’d be your boyfriend today, right? But I’m not quite feeling it… and I think it’s because of that.”

If Yamamoto-san were really my girlfriend, as we discussed at the platform, our relationship would revolve around lust. But with her holding back on sex, that key part’s locked away. Even if she’s okay with my naughty thoughts, as a guy, I can’t get fully excited without the prospect of going further.

“Oh, right, I forgot to mention something important. That issue? It’s already sorted.”

She handed me the popcorn bucket, wiped her hands with a wet tissue, and reached into her shoulder bag. From a palm-sized pouch—meant for makeup—came a string of square packets with circular bulges. Condoms. Too many to count at a glance.

“All set.”

Her voice rose with glee as she pulled out the strip to show me. Not just one or two—the entire pouch was stuffed with them. Ten? Twenty? Was she planning to use them all today? Am I gonna die?

“So, no limits on that front today?”

“Yeah… it’s why I’ve been so pent-up since yesterday…”

Her cheeks flushed slightly. Wait, when she said she was too excited to eat this morning, did she mean that kind of excitement?

“Well, that’s… good. I mean, sneaking anything in a theme park like this is probably impossible, so… looking forward to tonight.”

Miyu’s hunch was right. Good thing I rested last night. With Yamamoto-san, I’d be drained dry for sure.

“Of course, I’m not about to get it on in a crowded place like this…”

She leaned close, whispering in my ear.

“But I booked a hotel for tonight, so we can alternate between rides and sex if you want.”

Her sweet whisper hit my groin like a shockwave. Her voice vibrated at a frequency so erotic, I was on the verge of getting hard in public.

“I-I’ll think about it.”

I brought it up, yet here I am, flustered again. A cute girl carrying a bag full of condoms for a date? Too hot. Sure, I’ve been in a similar spot before, but that was half-joking, half-impulse. This girl’s serious. She’d probably make me fill every condom before letting me go, and she’s got the charm, skill, and stamina to pull it off.

My only worry is how easily she flipped from her strict “no sex” stance. But if she’s this eager, I can only see it as a blessing. I’m getting fired up too.

“Hehe, this is when I have the most fun with you, Sotomichi-kun.”

“I agree. But now I can only think about naughty stuff.”

“That’s fine, isn’t it?”

Yeah, I guess. Miyu’s the same way—both so casual about it. Are they sure they’re not half-sisters?

“What do you think if your boyfriend only stares at your chest?”

“What? That’s what they’re for.”

“Right.”

She could wear less revealing clothes despite her bust, so dressing like this must be intentional.

“Also, I kinda wanted you to feel a little superior.”

She meant the situation—guys around us stealing glances despite all the couples. Sure, the girls here are above average, but someone like Yamamoto-san is rare. With her picture-perfect erotic body, I’m probably earning envy or even secret resentment.

Most girls would hate leering eyes, but Yamamoto-san’s confidence lets her revel in it, giving her boyfriend a sense of pride. That bold self-esteem feels nostalgic. She’s finally back to her old self.

“Almost time.”

“Hehe, I’ve never been this excited for a ride.”

We finished the popcorn as we reached the front of the line. With crowds growing later, we’d hit popular rides first. Our first stop: the moving shooting game I wanted.

You ride an automated cart through a path lined with models, where 3D projections turn them into monstrous targets. You shoot them with a laser gun to rack up points.

What’s unique is the score display and branching endings based on your performance. The layout stays the same for a month, so even if you’re bad, a few tries can get you the best ending—a rare feature for a couple-focused park.

Groups launched one by one, grabbing laser guns from a stand and boarding slow-moving carts. Yamamoto-san and I took adult-sized gear and hopped in. The staff shut the door, and we rolled into a dark path, mission details blaring from speakers, which I tuned out.

“This is so exciting! Should I go all out today?”

“You don’t usually?”

“If I take out everything, it’s no fun for my partner, right?”

Fair point. At her level, she probably doesn’t miss a shot. Rumor has it only one group a month clears it blind, but she could do it effortlessly.

“Then let’s make it a competition.”

Feeling the cart’s vibrations, I reloaded with a satisfying click and aimed at a distant target. I’m good at games too. No backing down, even against her.

“You sure? I won’t hold back.”

“Bring it on.”

A deep boom echoed, the cave lit up, and evil souls animated the hidden monsters and statues. I raised my half-meter-long gun, peering through the sight, locking onto a target.

Instantly, six targets exploded in a chain reaction.

“What…!”

I tore my eyes from the sight to Yamamoto-san. She was calmly reloading, her face cool. Her aim time? Near zero. Factoring in the gun’s reload delay, she was hitting perfect shots, racking up points.

“You know the layout!?”

“Um… I can kinda tell by the sound?”

“No way…”

True to her word, she spun, locked onto a target behind her faster than me, and shot it down with precision. It was dazzling. She’s built differently. But—

“If that’s how it’s gonna be…!”

Predicting enemy spawns doesn’t just rely on sharp senses. Since their appearances are part of the ride’s design, they follow a human-like pattern. With decent game instincts, anticipating the next attack direction isn’t too hard.

“Here they come!”

A cluster of masks appeared in my line of sight, overlaid with hazy soul shadows, their eyes glowing red. Among the multiple simultaneous targets, I aimed at the center one—least likely to be hit first if you minimize wasted movement—and pulled the trigger.

The souls shattered, masks falling. But my gun’s counter stayed at “0.”

“You said competition, so I’m going all out to win.”

Yamamoto-san was merciless. She’d read my aim and sniped my target first.

Determined to score at least one point as a matter of pride, I focused hard. But Yamamoto-san perfectly tracked my aim throughout, crushing my resolve. Without wasting a single shot, she took down every enemy solo.

“Yay! Total victory!”

“Too strong… a monster…!”

It was unfairly overwhelming, almost refreshing.

“I seriously can’t beat you at anything except sex.”

“Even then, I’m supposed to be unbeatable. My specialty, maybe?”

“Compatibility’s a thing, huh?”

“Your sex is just too good…”

“That’s, uh, encouraging. …So, food?”

“Let’s go!”

Chatting on the way out, we decided to take a quick break. Cafes and restaurants dotted the park. Since we started early, we aimed for something hearty before lunch and eyed an Italian meat bistro.

“…Sotomichi-kun?”

My gaze locked on a couple at a terrace table, sipping a drink with a double straw—famous in dramas but rare in real life. The heart-shaped straws were so close, they could kiss if they leaned in.

“Hoh, Sotomichi-kun’s into cliché stuff, huh?”

“No, it’s not like that…!”

“Let’s do it! Next stop, there!”

Yamamoto-san dragged me to order a couple’s melon soda and plopped us at the terrace’s edge. A glass with a heart-shaped straw sat center table, a sandwich beside it.

“This is… nerve-wracking.”

“It’s got that lovey-dovey vibe! Miyu-chan would never.”

“True.”

Staring into a cute girl’s eyes while sharing a couple’s drink? A rare treat. Miyu would probably pout while sipping.

“Hehe, then, Sotomichi-kun, let’s… smooch!”

Yamamoto-san bit the straw, gazing expectantly. Green liquid climbed the tube, and I hurriedly took my straw’s end.

Her face was close. Big eyes. A girlish scent, distinct from the drink’s flavoring.

“Ugh… embarrassing…”

“Hehe, you’re adorable.”

She stared as if admiring me while I averted my eyes. Calming down, I met her gaze, and she flashed a bright smile.

I’m getting owned here. She likes me, and I’m her boyfriend today. I need to step up to make her like me more.

“You’re cute too, Yamamoto-san. Always thought so.”

I echoed her, realizing I rarely say it aloud.

“Oh. That’s sweet.”

Even she blushed, her gesture endearing. I let go of the straw, resting my cheek on my hand, faces still close.

“Those earrings really suit you.”

“Really? Thanks. Hearing that from you makes picking them worth it.”

They were new, chosen for today. She mirrored my pose, touching her earlobe.

“Why do earrings have a bad rep? Piercing feels self-harm-ish? Clip-ons don’t get the same flak…”

“Yeah, and I’ve been asked, ‘Your ex’s taste?’ a few times.”

“That’s rough.”

Maybe there’s a stereotype that “proper” girls don’t choose piercings.

“Wonder how I’d be without Miyu.”

I might’ve been a tactless jerk, prioritizing my feelings. …I’m still not great at tact.

“Whatever the path, you’re here, amazing, and dating me. I’m happy.”

“Oh…?”

Her embarrassing words mirrored my feelings about her.

“And we get to sip lovey-dovey soda.”

She sucked the straw again. I joined, our lips nearing. Hers looked glossy.

Kissing her would feel amazing. Her tongue’s probably as skilled as her blowjobs. I want to melt into her again.

(We’ve had sex so many times, but I’ve never kissed her…)

I’ve had countless hookups but can recall every kiss. Since Miyu introduced me to girls, my dating history’s order is all wrong.

I didn’t kiss Sachi, my first girlfriend. After our breakup, maybe it’s good I left her first kiss intact… Wait, no, Miyu took that too. Despite her disposition, how does she feel about casual sex? She’s with her brother now, so maybe she doesn’t care.

Yamamoto-san shows no sign of kissing me. Is kissing more special than I thought? Are our hearts not as close as our bodies right now?

“I think I know what you’re thinking, Sotomichi-kun.”

“What do you think?”

“I’m actually waiting for the right moment today.”

“Fireworks tonight, right?”

“Most romantic time.”

Our clipped conversation still connected.

“But, Sotomichi-kun…”

Staring close, she slowly closed her eyes.

“—!?”

Her thick, soft lips met mine. Brief, but my sensitive lips caught her warmth and the rich melon scent, overwhelming my brain.

“Ah… s-so sudden…”