I'm the Only One Who Doesn't Know My Sister is My "Stepsister" ~The Beautiful Twin Sisters Want to Seduce Their Oblivious Brother~ - 3

Chapter 3: The Sisters’ Plan

ーーーーーーーーーーーーーーーーーーーー

Studying was something she would never do and not to mention, she was being oddly honest too. Something was definitely off with Kairi, but… I decided to just let it go for now. 

“I-I’m going to my room then.”

“…Okay.”

I left the living room, leaving Kairi behind, who was acting weird. I had no idea what was going on here, but for someone like her, a blonde gyaru with constant red marks on her test, to suddenly study so diligently like that… It was just weird. So weird. Just what had happened? Did she eat something strange off the ground or something?

I went to my room and changed out of my uniform into something more comfortable while trying to assess the current situation. My twin sisters were beautiful. Their appearance made them stood out in the crowd. However, even though they were twins, but they were the complete opposite on the inside. They each had their own strengths and weaknesses. This was especially true in term of academic grades. The blonde gyaru, Kairi, who was studying in the living room, was nothing like our honor student sister, Yuuri. Kairi was always struggling with her studies. According to what Mom told me, Kairi was always tethering between the edge of repeating the year. She always received red marks after she entered junior high school. Mom used to work as a fashion model and although both Yuuri and Kairi inherited Mom’s stunning visage, but Kairi’s brain was… Underwhelming to say the least. A caveman might be smarter than her. The fact that Kairi was actually studying on her own volition was already strange enough, but she was being eerily meek to me too? Everything was so strange. 

“She even thanked me for picking up her socks… I haven’t heard her saying thank you to me since she entered junior high school. The last time she was nice to me was when we were still in grade school.”

Kairi had always been a bit stubborn and a tomboy. She always made Yuuri cry, but she was very attached to me. She was always nice and meek with me. 

“Well, she’s just your typical rebellious gyaru now though…”

I was changing my clothes while thinking about Kairi when there was a sudden knock on my door. I quickly finished changing into my loungewear and said. 

“You can come in now.”

And then, Yuuri, still donned in her school uniform, walked into my room.

“Welcome back, Onii-chan. I will be going to my cram school, okay?”

“Huh? O-Oh. Ye-Yeah. I see. It’s already the time for your cram school, huh.”

My little sister Yuuri, perfectly fit the image of the pure beauty type with her long black hair and gentle demeanor. She went to a nearby cram school and always made a point of telling me when she was leaving. She always left for her cram school at this time. 

Ah, right. Maybe I should ask Yuuri about Kairi. She might know something. 

“Hey, Yuuri…”

“Yes, Onii-chan?”

“You see… Don’t you think… Kairi is acting a bit strange today?”

“Strange…?”

Furrowing her eyebrows, Yuuri tilted her head to the side in confusion. My vague question seemed to make her confused. 

“We-Well… Kairi never studies, but earlier, I saw her studying math in the living room!”

“That Kairi is studying in the living room…? Hm? But she told me that she’s going to be calling her friend in the living room. So she told me not to step into the living room.”

Hm? Calling her friend was something Kairi usually did, but she wasn’t playing around like usual. Her action didn’t match with what she told Yuuri. I became even more confused. Maybe she wanted to study in secret? But if she really wanted to study, she should’ve asked Yuuri for help.

“Anyway, Onii-chan,there’s something I want to talk about with you. May I?”

“Sure, but why are you being so stiff with me?”

“Umm… I… I was being mean to you back then. You know, about the bathroom… I’m sorry for the way I said it.”

“The bathroom…? Oh. That.”

I remembered the time when Yuuri told me not to go into the bathroom right after her. She said I had to wait at least 30 minutes after her.

“I regretted it. I realized I must’ve hurt your feelings with the way I said it, so… I’m sorry!”

“No,no,no. I don’t think you were wrong though. I need to be more mindful from now on.”

“Thanks, Onii-chan. Actually… At that time… I was a bit more emotional than usual because it was close to that time of the month for me.”

“Oh… I-I see…”

Tha-Tha-Tha-That time of the month… Her period, huh. Seeing how red her cheeks had become, various thoughts started going through my mind. This just cemented the fact that Yuuri had become more womanly these days. Not just her chest or her body, but her inside was maturing too. 

“Me too. I apologize for being so insensitive. I will be more careful from now on.”

“No… It’s fine. But… With this.. We’re good now, right?”

“Ye-Yeah.”

Yuuri smiled pleasantly. 

“Alright. I will be going to my cram school then.”

She said before she ran down the hallway.

Crap. Yuuri was my little sister, but she was so adorable. But… Yuuri had become cold to me in the past few years. Not just recently. There was no way she was on her time of the month every day, right? 

While I was thinking about various things, my phone suddenly rang. It must be Mom. 

“Hello, Mom?”

“Ah, Yuuto? Sorry, I think I need to work until late tonight. Could you grab something from a family restaurant or something for dinner?”

“Okay. I will let Kairi know too.”

“Thank you~”

I headed back to the living room to find Kairi after hanging up the call. 

“Oi, Kairi. Mom’s going to be home late tonight—”

When I entered the living room, Kairi quickly tried to hide the textbook on the table with her body again. She was panicking again. 

“Knock next time!! Stupid Onii!!”

“No, but, people don’t normally knock when they walk into the living room!”

Kairi was still glaring at me, so I decided to ask her the thing that had been bothering me. 

“Why are you studying in secret like this to begin with? You should ask Yuuri for help if you want to study.”

“…Shut up!!”

Clearly angry at me, Kairi scratched her blonde hair before she stood up with the textbook in her hand and tried to walk past me. 

“Wait, Kairi! I think you’re a bit weird today—”

I grabbed her shoulder and Kairi immediately glared at me fiercely. 

Crap. She’s going to hit me. 

I braced myself and closed my eyes for the impending hit when suddenly, I felt something soft touching my lips. Something gentle and soft. 

Don’t tell me, this is a ki—

When I opened my eyes, I saw Kairi pressing her index finger against my lips.

“If you can’t keep your mouth shut, I will seal your lips like this.”

“Ka-Kairi?!?!”

Kairi brought the index finger that had just touched my lips to her own mouth, using the said index finger to touch her pink lower lip. 

O-Oi… Isn’t that basically an indirect kiss…

Seeing her gliding her finger across her own lips so sensually made a shiver run down my spine. 

“Yo-Yo-Yo-Yo-You!!”

“What? Don’t tell me… You’re feeling flustered? We’re siblings, right? This much skinship shouldn’t bother you.”

She said as she deliberately pressed her ample chest against my stomach. The sensation that reached my body was the most tantalizing sensation I had ever felt. Her breasts were softer than a beanbag and more elastic than the New Year’s mochi and the warmth of her skin made everything felt so realistic. Although just from a glance alone, I could tell she had big boobs, but this sensation made me realize with my entire body just how much she had grown. Her growth was astounding, not what I would normally expect from a third-year middle schooler. Her chest was nearly the same size as those busty gravure idols I often saw in magazines. 

“Onii.. If you will listen to my problem, I could do something… Even more amazing for you.”

Something even more amazing..

I gulped audibly. 

“We’re going to a family restaurant, right? Let’s talk there.”

So she said with a mischievous look in her eyes that made me suspect she was plotting something… Sinister.

ーーーーーーーーーーーーーーーーーーーー