My stepmother's burden is my ex-girlfriend.

But in my eyes at that moment, she had become an irreconcilable enemy.

...I really have to say, being in love is just a temporary infatuation.

I'm finally free from this confusion—

And so, with a light heart, free from burdens, I graduated from junior high school without any worries.

Then, that night.

My dad spoke to me with a serious expression:

--Dad is planning to remarry.

oops.

It seems that no matter how old a person lives, they can't escape moments of confusion. I couldn't help but feel sorry for this single father who raised his son alone, but I had no intention of objecting. Remarriage, great, please go ahead? It just so happens that I've also legitimately finished my compulsory education.

I was in a good mood at the time. So when my dad said that next, I inadvertently ignored it.

—The other person also has a child, a daughter…Don’t you mind?

Hey, I'm this old and I still have a stepsister? This is practically a light novel! Hahaha!

I actually got more and more excited as I listened. I guess I wasn't calm enough.

So a few days later, when my dad introduced me to my stepmother and stepsister, I felt like I'd been doused with a bucket of cold water.

──……………………

──……………………

The person in front of me is Yui Ayai.

wrong.

At that time, she had become Irito Yume.

We stared at each other, dumbfounded, both of us probably thinking the same thing:

—Damn God!

And just like that, my ex-girlfriend became my stepsister.

◆

"……I'm stuffed."

"Ayai—no, Yui said in a cold tone, then clattered the dinner dishes and took them to the kitchen."

...Damn it, the timing is terrible, I just finished eating. It's strange to keep sitting here silently.

"I'm stuffed."

I also stacked the dishes and went to the kitchen—where I saw Jie Nu washing her own dishes.

Her hair was so long it was annoying to look at, radiating a deliberately innocent, jet-black sheen. She was unhealthily thin; it seemed she'd be better suited to counting plates in a well than washing dishes in the kitchen.

The girl's long eyelashes drooped as she glanced at me. She didn't say anything, but simply clattered the bowls and chopsticks together.

I didn't have anything to say to her. I stood silently next to her and started washing the dishes.

I really didn't want to stand in the kitchen with this woman, but it wouldn't be right to completely avoid her. Because—

"Oh my, to be honest, I thought it would be difficult for a young man and woman to live together all of a sudden, but they seem to be getting along quite well, which is great."

"Yeah, right! Like today, Mizuto even went to the bookstore with Yume! Having the same interests definitely makes it easier to get along!"

"Now I'm relieved. After all, this was the thing that worried me the most."

My father and Jie Nu's mother sat at the dining table, chatting happily.

The two, who had just remarried, seemed genuinely happy every day—the complete opposite of our children.

"...Do you understand?"

"...Understand what?"

The girl next to me whispered to me, using the sound of rushing water as cover.

"You absolutely mustn't do anything that they'll regret."

"I understand. I'll take my relationship with you to my grave."

"very good."

"...Do you always have to be so condescending? When did you become like this?"

"If it wasn't like this before, then it's 100% your fault."

"What did you say?"

"What do you want?"

"Hey! What are you two talking about?"

My dad spoke to us from the dining room, which made us put away our sinister expressions.

"Nothing much, just talking about the books I bought today, nothing special."

"Yes, that's right. We were talking about books."

"—Ouch!"

As Jie answered in a cheerful tone, she secretly gave me a low kick when my dad couldn't see.

"(No need to repeat 'It's nothing.' How are your grades in modern Chinese (note: referring to the modern Chinese language subject in Japanese high school)?"

"(Unfortunately, my current national ranking is in the top 100 of the national mock exams. You know that, don't you?)"

"(...It's infuriating. What's infuriating is that I used to say things like 'Wow, you're so amazing~' and flatter you to the skies.)"

"(I'm also very angry. I'm angry that I used to humbly accept it.)"

On the surface, we play the roles of a well-connected step-sibling.

I can't let Dad and Aunt Yu-ren regret remarrying after finding out about our relationship—

This is the only consensus I have with Jie Nu.

Conversely, this also means that nothing else is valid.

As I was in my room reading the books I had bought that day, I heard someone knocking on the door.

"Dad? What's wrong?"

There was no response. Although I was halfway through my book and didn't want to be interrupted, I didn't want to dampen my newlywed father's spirits with a cold attitude—so I put a bookmark in the book, stood up, and opened the door.

Standing in the corridor is the woman I hate most in this world.

That is, Irito Yume.

"……What's up?"

I greeted Yui with "What's going on?", a greeting that came out when the temperature had dropped by about 100 degrees.

Jie snorted and raised her chin haughtily, as if to say, "This level of sarcastic remarks doesn't even qualify as a cold shoulder."

Let me use the most euphemistic way to describe my current state of mind: I really want to punch her.

"I have something to tell you. Are you free now?"

"How could I possibly have time? You probably already know what I bought today, right?"

"I know, that's why I came. Because I've already finished watching it."

“Tsk!”

It seems she came here specifically to distract me from reading.

Even when we were dating, this woman read a little faster than me. If we bought books at the same time and started reading at the same time, she would have already finished reading by the time I got to the climax.

Extremely insidious.

I just hate places like that.

Fortunately, they've already broken up.

"...What's wrong? Speak up if you have something to say."

"Let me into the room. I don't want Mom and the others to hear."

“Tsk!”

"Could you please stop clicking your tongue at me on purpose?"

"I'll stop as soon as you disappear from my sight."

“Tsk!”

Although I didn't see my dad or Aunt Yu-ren, I still carefully looked around the corridor before letting Yu-nv into the room.

As Jie Nu looked down at her feet, she walked into the room.

"Books are scattered all over the floor, it's a mess. Just being in this room is going to make me dirty."

"When you used to sneak into this room while my dad was away on business, your eyes lit up and you said, 'Wow, this is amazing...it's like a library!'"

"Life is so unpredictable. Even seeing the complete Sherlock Holmes collection neatly laid out now fills me with endless irritation."

"Go ahead and die. Watch me push you to the bottom of the waterfall like Professor Moriarty did."

I said dismissively, and sat down on the bed, which was half-covered by books.

"So? What do you want to tell me?"

"I can't take it anymore."

Jie Nu remained standing, speaking to me with a cold expression.

"I can't take it anymore—how much longer can I tolerate you calling me 'Yui-onna' so casually?"

I frowned. There was no need to hide my unpleasant feelings towards this guy.

"Don't you always call me 'Water Fighter' too?"

"I can call you by your name, but I can't stand it when you call me by my first name. Even when we were in junior high, I didn't let you call me that."

So you're not even willing to say the words "when we're dating"? Okay, I get it.

"Is there any way to address this? Someone taught us to use the same surname. Otherwise, how are we supposed to address each other?"

"Isn't there a more appropriate term?"

"What's your name?"

""sister"."

...Huh?

"We are siblings, so you should call me 'sister'."

"No, no, wait a minute."

I held my head.

"You? My sister? Mine?... Stop talking nonsense. It should be the other way around."

"Huh?"

"It should be 'older brother.' I'm your older brother, and you're my younger sister, okay?"

What nonsense is this guy spouting?

"...I'm really defeated by you. It seems my stepson's brain cells are on vacation."

"Believe it or not, I can give you a vacation? A vacation for life."

"Let me, someone who ranks in the top 100 in the national mock math exam, explain it to you. Listen carefully."

This woman is so good at math that she surpasses even the current nation's; she doesn't deserve to be a book lover. Unforgivable.

Jie Nu put on a teacher's air and raised her index finger.

"In this world, the one born first is the older sister or brother—that's the major premise. And I was born before you—that's the minor premise. Therefore, I am the older sister—that's the conclusion. Do you understand?"

The woman was smugly discussing logic, not mathematics, but there was something more important to me than that.

"...If I remember correctly, our birthdays are exactly the same day, right?"