The Protagonist's Sister Loves Me, But She's Definitely a Yandere. - Chapter 36: The Deduction Notebook

Chapter 36: The Deduction Notebook

“When I saw you carrying Runa on your back, I thought, finally! But I guess not~”

“…Yeah, well. Runa and I don’t have that kind of relationship.”

“Really? That’s a shame. If anything changes, you have to tell me! Promise!”

Youka-san was happily chatting away from behind the kitchen counter.

The stove was on, and she stirred a pot. A comforting smell of curry filled the air.

But since it was just the two of us, the conversation felt a bit awkward. Hinata didn’t seem like he was coming home anytime soon, and Runa was quietly resting in her room.

“Sorry for the trouble, Shinji-kun. It must’ve been hard carrying her all the way here.”

“No, not at all. The school’s really close to here.”

It was true. Runa was way too light. Of course, talking about a girl’s weight was off-limits, so I kept those details to myself. And the, uh… other stuff.

Like how I accidentally touched her thigh while carrying her. Yeah, better not mention that.

“How long are you planning to stay this time?”

“Hmm, well, if I don’t leave tomorrow, things could get a bit messy.”

“Tomorrow!? …That’s a really tight schedule.”

She came all the way back just to leave the next day? What kind of plan was that?

Youka-san was a career woman who worked all over the world. 

I didn’t know exactly what her job was, but I’d heard she was fluent in several languages. She might seem easygoing, but she was probably someone people relied on a lot at work.

“Her dad couldn’t make it back, so I wasn’t sure if I should come.”

“Was it because you wanted to see Runa and Hinata, even if just for a little?”

“Of course! If I can see my adorable kids, I’d come all the way from the Amazons!”

Her over-the-top love for her kids was well-known.

Honestly, she probably would come from the Amazon if it meant seeing them. The fact that she crossed the ocean just for one day made it seem like there was something important going on —but apparently not.

“I’ve been trying to get in touch with Hinata, but he’s not replying. He said he’d come home yesterday, but he’s being so distant. Hey, Shinji-kun, do you know where he is?”

“He’s probably busy with plans. Hard to say.”

I wondered if Youka-san knew about Hinata’s little harem situation. If she, someone who was devoted to her husband, found out about Hinata’s current status… a chill ran down my spine just thinking about it.

I took a sip of the tea she had prepared, carefully avoiding the topic.

“Oh, you’re staying for dinner, right? I made your favorite —spicy curry.”

“…Alright, I’ll take you up on that. I’ll let my mom know.”

“No need! I already told her, and she said it’s fine.”

She sure worked fast behind the scenes. I turned my phone off again and let it fade to black.

A dull variety show played on the TV, just background noise. Outside, the night had fully settled in. If you just looked at this moment, it seemed peaceful. I let out a long breath.

I’d always known I talked to myself a lot, but lately, I’d been sighing more too.

“When Hinata gets back, should we have dinner then? Or do you want to eat now?”

“Hmm… let’s wait a bit longer. Tomorrow’s a day off, after all.”

“Oh, right! Today was the sports festival, wasn’t it? Tell me all about it!”

Youka-san wiped her hands and turned halfway around. The sports festival had been open to the public, but her flight schedule meant she couldn’t make it. She looked genuinely disappointed.

I started sharing little bits about Runa’s and Hinata’s performances.

“Wow, so you were helping out as a committee member too, Shinji-kun!”

“I was just getting dragged around by Runa. I didn’t really do anything.”

“Come on, don’t be so modest. You’ve always been like that since you were little.”

She was one of the few people who knew me as a kid. Hearing about those days made me feel awkward. There were probably things I didn’t even remember myself. I just nodded, hoping to end the conversation.

Youka-san chuckled softly, then, as if she remembered something, turned off the stove.

“Oh, it should be ready soon.”

Saying that, Youka-san started preparing something in a bowl.

I watched curiously as she placed a steaming bowl on a tray and set it down in front of me with a thud. The smell of broth filled the air. When I looked, I saw it was udon.

“Here, take this to Runa.”

So, I was supposed to deliver this to her before we ate curry?

I wasn’t exactly the type to complain about food, but I tilted my head in confusion.

“…This is for?”

“For Runa. I told her to leave her door unlocked.”

“I see. But… me going into her room…”

Runa’s room had been locked most of the time for the past few years.

Even though this was an emergency, it still felt wrong for me to just walk in. But Youka-san seemed to understand how I felt and patted my shoulder reassuringly.

“It’s fine, it’s fine. She’s a teenager, sure, but she’s sick right now.”

While I was still trying to figure out how to respond, she added more.

“I think she’d be happier if you took care of her instead of me. Oh, and here —cooling gel packs and medicine. She already has a thermometer, so if she’s awake, get her to check her temperature.”

Youka-san returned to the kitchen, leaving me with no choice.

All that remained was me, the steaming bowl of udon, and the tray.

If Runa wanted to see someone who’d make her happy, it was probably Youka-san, since she hadn’t seen her in a while. But Youka-san just hummed a cheerful tune as if everything was settled.

I sighed, giving in to my fate, and picked up the tray before stepping into the hallway.

The cool air from the AC leaked through the gap under her door. The warm, stuffy air clung to my skin, making me uncomfortable. The thought of it getting even hotter wasn’t helping my mood.

Carefully, I climbed the stairs, making sure not to spill anything, and headed to the end of the hallway.

“Runa, can I come in?”

I asked softly. No reply. Balancing the tray with one hand, I knocked on the door.

After waiting a few seconds, there was still no answer. I turned the doorknob, and sure enough, it wasn’t locked. She must’ve used the last of her strength to unlock it.

It had been so long since I’d entered Runa’s room that I couldn’t even remember the last time.

“…I’m coming in.”

I pushed the door open. It let out a sharp creak.

The first thing I saw was a white comforter. It was puffed up in the shape of a person, with just her head peeking out. Her face was flushed, and she was breathing heavily. She looked miserable.

Beside her pillow, a few stuffed animals were lined up neatly.

“…Where should I put the tray?”

Even though I felt a little bad about it, I glanced around the room. Bookshelves, a study desk, and some makeup items —a mix of student life and a reminder that she was a girl. It made me feel uncomfortable.

The cute color scheme of the room didn’t help either. My mental stamina was taking a hit.

“Uh…”

The person herself groaned softly, breathing heavily.

The blanket rustled as she shifted her legs underneath it. Carefully, trying not to make any noise, I placed the tray on her study desk. The shelves above it were packed with notebooks and reference books, all neatly organized.

Now what? It felt wrong to wake her up.

But if I left things as they were, the udon would get soggy.

After hesitating, I decided to call her name. If she didn’t wake up, I’d leave her alone. In that case, I’d just ask Youka-san if I could eat the udon myself.

“Runa, I brought some udon. Do you feel like eating?”

I gently shook her shoulder and called out to her.

Runa made a small sound from her throat. Even while sleeping, her delicate face didn’t lose its calm expression.

Maybe she was fighting off the fever; sweat was trickling down her forehead. I took the face towel Youka-san had given me and wiped it away. That seemed to do the trick.

Runa slowly opened her eyes, staring blankly at my face.

But her gaze was unfocused, and she seemed to be drifting between reality and a dream. Then, in a dazed voice, she muttered her first words:

“…Mom? I’m not hungry.”

She gripped my hand tightly. It felt much hotter than when I was carrying her earlier. Normally, just holding her hand would make me flustered, but today, all I felt was a rising sense of worry.

It seemed like she was mistaking me for Youka-san. That only made me more concerned.

“Pushing yourself too hard. Okay, here comes something nice and cool.”

I gently loosened her grip and placed a cooling pad on her forehead.

“Eek.”

She let out a cute little squeal and flinched slightly. But the next moment, her eyes relaxed, and she looked like she was enjoying the relief. Just like a cat.

But at this rate, eating udon seemed out of the question. I figured I’d eat the udon with the curry later and ask Youka-san to give her some nutritional drinks or soft foods instead.

“I’m leaving the medicine here. Take it when you wake up.”

Staying in her room any longer would probably make it harder for her to rest. I didn’t want to get in the way, so I decided to quietly leave. Hopefully, she’d get better soon.

“…Mmm.”

Just as I was about to leave, Runa pinched my shirt softly. Thinking she called me, I turned around.

She was still lying there with her eyes closed, breathing heavily.

“…Runa?”

I gently unhooked her fingers. 

She seemed to be half-asleep. But when I tried to leave the room again, she grabbed my shirt once more, as if she wouldn’t let me go. Even in her dazed state, I could feel her firm determination. 

I smiled —it was just like her.

There was no helping it. I decided to stay until Runa fell soundly asleep. The udon would get soggy, but that was a small matter.

“Alright, I’ll stay here until you fall asleep.”

Hearing that, Runa smiled contentedly. I’d seen her sleeping face at the sports festival too. If the boys at school knew, they’d probably be so jealous they’d want to stab me —the thought made me shiver.

I sat down on the chair she probably used every day.

It felt wrong to look around the room too much. Even close friends have boundaries.

But I had left my phone in the living room, and now I had nothing to do.

As I watched her sleeping face, something caught my eye —a textbook on her desk. It was familiar; it was one I used when I was a first-year student, which I had given to Runa.

I picked it up and noticed the corners were slightly dirty and worn down.

“…You’ve really been using this a lot.”

That made me feel a quiet sense of happiness. It was probably like when a senior in a club passes down something to a junior.

I’d never joined a sports club, so I wasn’t entirely sure, but it seemed right. Knowing something I passed on was being used and treated with care made me smile.

“Hm?”

After putting the textbook back on the shelf, my eyes were drawn to two notebooks. They were kept in a separate section, away from the other textbooks and reference materials.

Feeling a bit guilty, I picked up one of them. There was no title on it.

I glanced over at Runa. Her eyes were still closed.

Usually, I wouldn’t even think about snooping, but with nothing else to do, I couldn’t stop myself from flipping through the pages. If it turned out to be too personal, I’d put it back immediately and apologize later.

But I couldn’t stop turning the pages. This was…

“…Stalker countermeasures. Ways to get closer to Shin-nii.”

It listed strategies and the potential outcomes, all neatly in bullet points. Analyses and predictions were written out, clearly showing her efforts to uncover the stalker.

Runa… she made this notebook to help me? I didn’t know what to say. A strange mix of emotions filled me —relief and a quiet sense of happiness. Yeah, it was mostly relief.

The notebook detailed dates, actions, and plans for what to do next.

If Runa were the stalker, she wouldn’t need something like this. If she wanted to clear herself of suspicion, she could have just shown me this notebook directly.

The fact that she was doing her own investigation made it clear: she was almost certainly innocent.

Of course, there were still things like the missing handkerchief and other incidents that needed answers.

I gently put the notebook back and let out a breath of relief. The chances that Runa was the culprit were low. That meant Mimi or someone else was now the most likely suspect.

“—And this one…”

My eyes fell on the other notebook. It looked like it could be a continuation of her detective notes.

But going through more of her stuff without asking didn’t sit right with me. I hesitated for a moment, then let my hand drop and quietly stood up.

“…Suu… suu…”

Before I knew it, Runa had fallen into a deep sleep, her breathing soft and steady.

I noticed one of her arms had slipped out from under the blanket. Gently, I tucked it back in and pulled the blanket up to cover her properly. She shifted slightly, as though trying to escape the heat, but she needed the warmth.

This small body had been through so much stress and exhaustion.

I’d dragged her into this mess, and she’d helped me more than I deserved. 

When this whole stalker situation was finally over, I’d find a way to thank her properly.

That was a promise I made to myself.