My Little Sister Suddenly Confessed to Me, but What Am I Supposed to Do by Dating My Little Sister?

Chapter 102: Yuu, Shiori, and Mitsuki

There was a knock at the door…

“Come in~~”

The knock was different from Onii-chan’s. Mom isn’t home today, so it’s probably Mitsuki-chan…

“Onee-chama, do you have a minute?”

It was Mitsuki-chan, as expected. I thought she’d probably come. If it’s Onii-chan, he can save Mitsuki-chan… When they came home today, Mitsuki-chan’s atmosphere had changed. I didn’t ask, but… Onii-chan probably saved her… Onii-chan really is amazing!! But…

And Mitsuki-chan is still wearing Onii-chan’s T-shirt… I’m so jealouuuusssss!! Even I can only wear it in secret… and of course, it’s a used shirt… Ehehehehe.

“…Yeah, come in, Mitsuki-chan.”

I pulled myself together and let Mitsuki-chan into my room. As soon as she entered, she looked around curiously.

“Onee-chama’s room is pretty normal. I thought there’d be huge photos of Niichama on the walls.”

Photos of Onii-chan? I’d never put those on display. I’ve digitized all his old photos to prevent deterioration and made multiple backups. The negatives and prints are stored securely.

I keep all recent photos saved digitally too—on my PC and phone, filling them to capacity. But I don’t look at them much. Because when I close my eyes… Onii-chan always appears. Ah, Onii-chan… Kyaaaaa! This Onii-chan is so handsome…

“Um… Onee-chama… you’re drifting off to an Isekai again…”

Onii-chan, Onii-chan, Oniichaaan! Ehehehe!!

“Ah! S-sorry… Um, have a seat, Mitsuki-chan.”

I had Mitsuki-chan sit on the panda cushion at my round table. I also have a bear cushion, but that one is for Onii-chan only since he sat on it once. No one else may use it…

I poured some oolong tea I’d brought to my room into a cup.

“It’s probably a bit warm.”

I handed it to Mitsuki-chan. She shook her head to say it was fine, took a sip, and looked straight at me.

“Um, Onee-chama… thank you for today. For letting me be alone with Niichama…”

“It’s fine… But Mitsuki-chan, you’re calling me ‘Onee-chama’ instead of ‘Shiori-neechama’ today?”

It was a subtle change. She’d occasionally slip and call me “Onee-chama” before, but today she’s been doing it consistently…

“Yeah… Onee-chama… thank you… I was so happy.”

She suddenly thanked me. Something I’m being thanked for… could it be…

“Um? For what?”

The only thing I did was give her alone time with Onii-chan, right? That would make her happy, obviously. Uuuu, I’m so sad! This feels like my heart is being torn apart!

“Today, Niichama hugged me…”

Mitsuki-chan closed her eyes and hugged herself… !!!!!

“Wh-wh-wh-wh…”

Noooooo! Onii-chan… Onii-chan… I knew it… The reason he wouldn’t make a move on me… was because… Waaahhh! Onii-chan became a lolicon! Eh? What should I do? Should I ask Shiroi-sensei how to stay a loli even as an adult…?

“Ufufufu, it’s okay, Onee-chama. I was just teasing. Niichama didn’t mean it that way.”

Mitsuki-chan started laughing at my panicked state… Uuuu, “didn’t mean it that way”… what way…?

“…Um, I wasn’t worried about that at all. Not even a little bit…”

“Fufu. Onee-chama, you really stop being amazing when it comes to Niichama.”

“Uu, I’m not amazing at all. Onii-chan is the amazing one…”

“Yeah… it’s really true… Today, when Niichama hugged me, he told me I’m his sister, his family. He said you said the same thing. He said if I’m lonely, he’ll always be with me. I was so happy. I cried because I was so happy… Niichama is so, so warm…”

“I have my grandma—oops, Yayoi-chama—and Mom and Dad, and now I have Onee-chama and Niichama too. If I say I’m lonely after all that, I’d be punished, wouldn’t I? Onee-chama… thank you for making me your sister. Onee-chama… I love you!!”

Mitsuki-chan lunged at me with the agility of a rabbit. The momentum made me fall back onto the bed, hitting my back.

“Kyaaa! Mitsuki-chan, that hurt~~ I hit my back!”

“Ehehe, Onee-chamaaa!”

Mitsuki-chan nuzzled her cheek against mine. She’s so cute~~ Little sisters are so cute~~ …Wait!! Is this it?! Is this the feeling of finding a little sister cute?! If I use this on Onii-chan, maybe he’ll think I’m even cuter~~ Thank you, Mitsuki-chan!!

“But, Onee-chama…”

Mitsuki-chan, still clinging to my neck, whispered in my ear…

“I won’t give Niichama to you… Mitsuki can’t live without him anymore… I love you, Onee-chama. I know you love him to death too. But I won’t give him up. I know you’re dating Niichama. So…”

Mitsuki-chan let go of me, straightened her back, and sat in seiza. Her smiling face from moments ago turned into a serious gaze.

“I love Onee-chama! But I love Niichama even more. So, to my beloved Onee-chama, I, Mitsuki, hereby declare war! I will steal Niichama from you!!”

I sat in seiza in front of Mitsuki-chan and straightened my back the same way.

“Mitsuki-chan! I will absolutely never give up Onii-chan! I won’t hand him over to anyone!! I accept your declaration of war! …Bring it on!!”

I took a fighting pose toward Mitsuki-chan.

After staring at each other, we both burst out laughing. Not in a way that suggested we were joking, but in the way comrades laugh when they’ve found a kindred spirit.

“But, Mitsuki-chan… Onii-chan has been getting pretty popular lately… If we’re too busy fighting each other, someone else might swoop in and steal him…”

“You mean someone’s aiming for the ‘fisherman’s profit’… Ah, Michiru-chan and Asami-chan, right? And that Student Council President too… All beautiful women… They’ll be tough opponents…”

“Yeah. And also our homeroom teacher… She’s really cute, and she’s even received a love letter from Onii-chan…”

“Onee-chama…!!”

“Mitsuki-chan…!!”

Mitsuki-chan and I shook hands…

“For now…!”

“Yeah!!”

“Let’s cooperate!!”

With this handshake, we concluded a pact to prevent anyone else from taking Onii-chan. We declared war and immediately signed a ceasefire treaty… As expected of cousins, we really are two of a kind…

Chapter 103: Legal!

“Sorry, there was a movie I really wanted to see, so head home without me.”

I pressed send and turned off my phone. I didn’t actually have a movie to see; I just wanted to be alone for a little while.

I don’t know what happened, but ever since we got back from Haneda, Shiori and Mitsuki have been suspiciously close. It’s beyond just getting along; they have the aura of actual sisters.

I mean, it’s fine. I’m glad they’re close, but… it feels like they’re conspiring.

Lately, it feels like I’m under a constant 24/7 pincer attack from those two. I can’t do anything. Even today, I was dragged along for shopping, only for them to start giddily picking out underwear together.

I couldn’t stand being there, so I told them I’d be at the bookstore. As soon as I stepped out of the department store, I saw a manga cafe. The urge to just read books in peace was irresistible.

I felt guilty, but I lied about the movie to justify turning off my phone and ducked inside.

Men—and women too, I think—will understand. No matter how much you love someone, you need a little “me time.” Not necessarily in a physical sense, but for your mental health.

So here I am, finally enjoying some reading time. Piling up books and manga, coffee in hand, noise-canceling headphones on… bliss. In middle school, this was my entire life. Now, it feels like a precious luxury. Call me spoiled if you want, but this is the best.

“Crap! I stayed for five hours… I’m terrified to turn my phone back on.”

It was pitch black outside. We don’t have a strict curfew, but if I’m too late, Shiori gets angry. And man, can she get angry. Her pouting is cute, but her scolding is real.

As I hurried toward the station, I saw a police officer arguing with someone.

“Listen, kid, you look like a middle schooler. Are you drinking?”

“I’m… an aduuuult! Zo, I can drink if I waaaant!”

“What kind of adult dresses like that? If you’re serious, show me some ID!”

“Ehhh? Are you hitting on meee? Too bad for youuu, I already have a person I loooove!”

Dealing with a drunk like that sounds like a nightmare, I thought as I tried to walk past. But then, I caught a glimpse of twin-tails peeking through the officers… those twin-tails look familiar. “Sensei?”

The moment I spoke, everyone turned to look at me. Ah, dammit.

“AAAAAAAAHH! It’s Yuu-kuuuuuuun!”

I really screwed up this time.

I ended up explaining the situation.

“A high school teacher? No way… seriously?”

I nodded.

Shiroi Satomi stood there, swaying and smiling at me. It looked like a member of Judgement was being interrogated by Anti-Skill.

“Sensei, don’t you have your ID?”

Without it, she’s definitely going to be taken into custody. Especially in those clothes.

She had twin-tails with big red ribbons and a pink floral dress. She’s barely 140cm tall. Even with heels, she’s tiny. She looks like a middle schooler—no, an elementary schooler.

“I have my… teaching license!”

Why the hell are you carrying that around?

Satisfied by the license and my confirmation, the Anti-Sk… I mean, the police officers, left.

I looked at Sensei. She was wobbling on high heels, clearly trying to look taller. It was dangerous to watch. I stepped closer and took her hand.

Seeing her beam at me as we held hands gave me a sense of happiness, like a parent walking with a child… Wait, this woman is ten years older than me, right? In some ways, she seems younger than Mitsuki.

“Ufufu, hey, Yuu-kuuuun, let’s go drinkinnnnng!”

It’s no use; she’s completely wasted.

“If a high school teacher takes a student drinking, they’ll be fired on the spot.”

“Ehhh? Who cares about getting fired?! I’m a free spiriiiit!”

“No, that’s definitely not okay.”

“Fine theeeen, let’s go eat somethinnng! Big sis will treat youuu!”

She thumped her flat chest. It’s a close match with Michiru.

“No, I really have to get home…”

“Ehhhh?! Fine then! I’ll just invite that random old guy over there! Hey! Mister!”

“Whoa, whoa! Stop! A teacher shouldn’t be doing that in front of a student! Look, you’re scaring him!”

In this day and age, no man is brave enough to take up an invitation from a girl who looks like a child.

“Then you go with meee!”

“I really have to go back…”

If I’m even later, I don’t know what Shiori and Mitsuki will do to me.

“Uuu… waaaaaahhhh! Yuu-kun is rejecting my request againnnn! You used to be so cute! You said you’d marry meeeee!”

Here we go again. I’m a high schooler making a “child” cry in the middle of a busy district. What a situation. Judgement is going to come for me… oh wait, she’s already here.

“Alright, alright! I’ll go! I’ll go anywhere, just stop crying!”

“Really?”

She looked up at me with teary eyes. What is this cute creature? Is she really an adult?

“Yes, yes. Where are we eating, Sensei?”

Whatever, Shiori and Mitsuki are going to be mad anyway. Being a little later won’t change the punishment much.

“Yay! This wayyy!”

She pulled me along. Well, she was so wobbly I was the one supporting her.

We walked in the opposite direction of the station. After ten minutes, we reached a large apartment complex. An apartment?

She unlocked the auto-gate, we took the elevator, and she pulled me into a room.

“Wait… is there a restaurant in here? …Like hell there is! This is your house, Sensei!!”

“Welcoooome, Yuu-kuuuun!”

Sensei turned around and beamed at me.

Ah, things are getting troublesome again…

Chapter 104: Legal!!

“Hurry, hurry, come in already!”

Sensei pulled me forcefully into the apartment. Wait, my shoes—am I supposed to take them off too? I was dragged into the living room and told to sit. It was a surprisingly nice place; do teachers really make this much money?

“Okay, Yuu-kun, wait just a second, okay?”

As she said that, Sensei grabbed the hem of her dress and started pulling it straight up over her head! EEEEEEHHH?!

Black lace underwear was revealed, and I caught a glimpse of her bra before I could process—

“HEY! Stop right there! What do you think you’re doing?!”

“Fue? I’m going to cook for Yuu-kun now, so I need to change…”

Her speech pattern has turned into a slow drawl like Asami’s. No, that’s not the problem.

“Change in another room! I’m sitting right here!”

“Fue? You can watch if you want.”

Good grief, every girl lately is trying to strip in front of me. I’m seriously going to snap one of these days…

“Just go change in the other room!”

I practically shoved her out of the living room. I’m exhausted… I thought about slipping away, but I can only imagine a future where she chases after me crying…

Wait… black lace… no, I’ve seen that in anime… but still… Is she going to come back out in a frilly negligee?

Contradictory to my expectations, she returned to the living room wearing a simple sweatshirt.

“I’m gonna cook now, so waaiit for me~~”

She headed to the kitchen. She’s still wasted; is it even safe for her to be in there? I followed her, only to find her swaying unsteadily with a kitchen knife in hand.

“Sensei, that’s dangerous.”

“Don’t call me Sensei~~ call me Satomi!”

She pointed the knife toward me while intimidating me. That’s legitimately terrifying.

“No, put it down! You’re going to get hurt.”

“It’s fiiiiine. It’s mostly pre-made stuff anyway.”

She twirled the knife skillfully. It was scary, but her movements were surprisingly adept. Does she cook often?

I waited in the living room for a few minutes.

“Heeere, it’s doooone.”

She brought out a tray with several dishes. They actually looked delicious. Meat and potatoes (nikujaga), potato salad, potato gratin… why is everything potato-based? And it’s a weird mix of Japanese and Western styles…

“Here, Yuu-kuuuun, eat up.” Kshh!

Kshh?

“S-Sensei, are you still drinking?”

“Ehhh? It’s orange juuuiice…”

The can clearly said 8% alcohol.

“Is it tasty?”

She stared at me with glazed eyes. I felt like I was watching a middle schooler getting drunk—an “illegal” sight, despite the “legal” reality.

I tried the nikujaga. It was amazing!

“It’s good. You’re a great cook, Sensei.”

“Ehehe. I’ve always been good at it. I wanted Yuu-kun to eat my food.”

She kept drinking that “orange juice” at a steady pace while watching me eat.

“Yuu-kuuuun, hey… Yuu-kuuuun, why are you… so cute?”

“Pfft! Wh-what are you saying all of a sudden…”

“Hehehe, you’re so cute~~”

Seriously, stop it. Being called cute by an older woman feels… complicated.

“Hey, I have… one thing I want to ask…”

Sensei’s gaze turned slightly serious.

“Are you and Shiori-san… really siblings?”

Where did that come from?

“Of course we are. We’ve been together since we were babies. I’ve seen the photos from when we were tiny…”

I’ve never even entertained the thought that Shiori and I weren’t related.

“Hmm… but Shiori-san and Yuu-kun don’t look alike at all, do they?”

“Well, obviously. She’s a beauty, and I’m average at best.”

“No, Yuu-kun is cute! But I’ve seen many siblings, and I’ve almost never seen a pair as different as you two.”

“…………”

“Also, being born only a year apart is actually difficult, you know? The postpartum infertility period…”

“Stop it!!”

“Y-Yuu-kun…”

“Shiori and I are siblings.”

“Yeah… sorry. I’m sorry…”

“No, I’m the one who’s sorry, Sensei. I should get going. Thanks for the food.”

I stood up and headed toward the entrance.

“Yuu-kun, do you love Shiori-san?”

She called out from behind me, but I didn’t answer. I put on my shoes and opened the door. Sensei stepped out with a troubled expression. I gave her a nod and stepped out.

“Yuu-kun, I… about you…”

She tried to say something just as the door was closing.

“No, never mind. Thanks for walking me home.”

“Thanks for the meal, Sensei.”

I closed the door.

Walking home, her words echoed in my head. I’ve looked into that before, even without being told. But the return of a cycle varies by person; for some, it returns in a month.

Besides, I’ve seen definitive proof that we are siblings. As long as that exists, there’s no way we aren’t related.

I stopped thinking about it. Instead… wait, did I just miss a once-in-a-lifetime opportunity? I was fooled by her appearance, but I was alone with an adult woman in her apartment, and she even stripped to her underwear… A teacher and a student… Was that a “served on a silver platter” situation?

“Did I fail…? No, no, no.”

If I got caught, Shiori would kill me. And now Mitsuki is there too… they’d probably achieve the perfect crime. Either I, Sensei, or both of us would be erased. Thinking about that, I felt a wave of relief that I hadn’t taken the bait.

I opened the front door to my house. Huh? No one’s here? I expected the two of them to be standing there waiting for me…

The first floor was silent. Are they on the second floor? It’s too early to sleep, and Dad isn’t home yet. I went upstairs and opened my bedroom door…

“Um…………”

The two of them were lying in my bed. Why?

“O.”

“O?”

“Onii-channnnnn!”

“Niichamaaaaaa!”

The moment I reached the bedside, they jumped up, grabbed my arms, and dragged me onto the bed! And why are they both in their underwear?!

Seeing them both sleeping in their underwear… is this the “Kimashi” moment of the story?!

“Onii-chan, look! These are the ones we bought today! Look closely!”

“Niichama, look at these children’s panties! You like these, right?!”

“I’m not looking and I don’t like them!!”

The two of them froze.

“Onee-chama…”

“Yeah, Mitsuki-chan…”

They checked in with each other. What now?

They sat up—seriously, don’t sit up like that!

“Onii-chan, sit there…”

They pointed to the floor. I sat cross-legged, looking down to avoid seeing them.

“Niichama!! Seiza!!!”

Mitsuki commanded me with an terrifying amount of pressure. This elementary schooler is scary!

I shifted into seiza. Shiori began speaking like she was in a courtroom drama.

“We will now begin Onii-chan’s trial. Prosecution, your statement.”

“Niichama abandoned us, his sisters, today. This is a grave act of betrayal. Furthermore, despite claiming to go to a movie, he went to a residence belonging to a woman, adding further to his crimes. He must be punished severely to atone!”

“Defendant Onii-chan, your response?”

“Wait, wait! A judge can’t conspire with the prosecution! And do you have evidence that I lied? I demand a lawyer!”

“Oh, we have the evidence right here, Niichama.”

Mitsuki shifted into a period-drama tone. What, are you going to show me a cherry-blossom tattoo? You’re already in your underwear…

“Onii-chan… I can smell a woman’s scent on your arm. And your body smells like alcohol…”

“Yeah. Also, the area near Niichama’s hands smells like nikujaga and gratin, and his clothes smell like a woman’s house.”

“And there are no movies currently showing that match your tastes enough to abandon us. We figured you probably just wanted to read books in peace.”

“So, we decided we wouldn’t be mad if that was it. We were going to surprise you by sleeping here together, but then… NIICHAMAAAAA!”

“Now, Onii-chan. Tell us exactly where you were, who you were with, and what you were doing.”

Mitsuki looked furious. Shiori was smiling.

What are these two, dogs? They have the sense of smell and analytical ability of police dogs… I’m completely defenseless. Infidelity is impossible. I’m so glad I didn’t “eat the meal” at Sensei’s place… they would have known instantly.

“Speak, Niichama!!”

“Onii-chan, I won’t get mad… so just tell us, okay?”

This interrogation… it’s probably stricter than the actual police. But as I wondered how long I could hold out, I found myself actually starting to enjoy it a little…