My stepmother's burden is my ex-girlfriend.

"Ah, you're out! Your reaction is enough to get you out! A normal brother or sister wouldn't blush just because they're called on!"

"...I'm not shy at all."

"It's obvious! How many times do you think I've seen that look on your face?!"

"Whatever. I think you've mistaken me for someone else. I only met you a few days ago."

"You're so deceitful! You ...!"

I stubbornly refused to turn my face back to face the girl who was stomping her feet like a child. Although I didn't feel my face burning, my heart racing, or want her to call out again, putting all that aside, I had no obligation to turn my face to her.

The girl was still protesting, but she was making a bit too much noise.

"Yui--? What are you shouting about--?"

Aunt Ren's voice came from downstairs, and it felt like a savior to me. I beamed with pride, celebrating my victory.

"Time's up—"

"Ugh, waaaaaah...!"

"Hey, if you've learned your lesson, don't try to mess with me again next time. You might be misunderstanding things because you've read too many mystery novels, but you're not on the same level as me."

This is it, right here. I tapped my temples with my fingers.

Whether from anger or frustration, Jie's face turned even redder, eventually becoming teary-eyed.

"...You never used to talk to me like this, bullying me...!"

...Don't cry, that's despicable.

I awkwardly fiddled with my bangs.

...Perhaps I got a little carried away. Using book categories as a pretext to attack someone is the most vicious personal attack against people like us. My actions are no different from the media randomly searching through criminals' bookshelves and spouting nonsense. Hmm, perhaps I really went too far...

After a sigh, I reluctantly and after struggling for a long time, I finally reached out my right hand and gently patted Jie Nu's head like I was coaxing a child.

"Okay, okay, it was my fault, I'm sorry. Sister—uh—older sister."

...I miss those days. I used to do this every time something happened, and then admire Ayai's shy expression—

However, at this moment, Jie Nu showed no sign of shyness whatsoever.

She trembled violently, like a volcano about to erupt.

"………………At once……"

"At once?"

"It's... this kind of place! I hate it when you do things like that so casually! You stinky older brother!"

After uttering a strange and harsh remark, the girl tripped over the tower of books and rushed out of the room.

I couldn't react in time; someone was left behind.

...I've never seen her react like that before, even when we were dating.

"...Really..."

--Me too, okay?

Someone like you—introverted yet fiercely competitive, seemingly mature yet still a bit childlike…showing a side of yourself never before revealed to others when they least expect it—

—I just hate places like yours.

◆

In terms of results

"...Good morning, Mizutani."

"...Good morning, Yume."

The way of addressing them remains unchanged.

It was agreed from the beginning that if the rules were broken, one would only have to act as the younger brother or sister once. Otherwise, it would turn into a mysterious relationship where they call each other "older sister" and "older brother".

If I had to point out where things have changed—

"Mizuta, could you get me some soy sauce?"

"Oh, okay, Yume."

When I handed her the soy sauce bottle, our eyes met for a fleeting moment.

—I'd rather die than be your sister.

—What a coincidence, I would rather die than be your younger brother.

These thoughts are left unsaid.

I don't get along with this girl. Those days in junior high were a mistake; we were just temporarily lost. The lesson learned from yesterday's events is that we understand this more clearly now.

We sat down together for breakfast, greeting each other with low kicks under the table. My dad and Aunt Yu-ren, sitting next to me, seemed oblivious, chatting and laughing affectionately.

Only we know about our relationship.

Knowing that a family living under the same roof is actually the most hated, irreconcilable enemy in the world.

...But then again...

"Yui, give me back my soy sauce."

"Okay, water bucket."

Even though we always addressed each other by our surnames while we were dating, we ended up addressing each other by our first names after we broke up—making me think that God really knows how to be sarcastic.

Volume One: Past Romantic Relationships Remain Unresolved; Couples Must Guard the Home – "What's so strange about me doing this in my own home?"

Looking back, I can only say it was a mistake I made when I was young. However, I had what is commonly known as a boyfriend between my second and third years of junior high school.

The man had a pathetic appearance, didn't care much about his appearance, was always a bit hunchbacked, and spoke without any humor. He was a complete social outcast, utterly lacking in masculine charm—but well, he wasn't stupid.

However, at the time, I was in my second year of junior high school—a perfect stage of adolescence and an unparalleled country bumpkin. Just because he treated me a little gently and we got along fairly well, I couldn't help but feel a little happy—and I was overjoyed.

It was truly a case of carelessness leading to disaster.

It can be said that this was a mistake made when one is young.

Ever since I wrote a love letter in a fit of excitement in the middle of the night, and then impulsively gave it to him, my destiny has been paved all the way to its end.

The only outcome for a junior high school student's relationship is "breakup".

After all, this isn't some shoujo manga for kids—the two of them will eventually come to their senses, remember the reality, and then break up as if nothing happened. That guy and I were no exception; we ended up on that path.

Then, our parents remarried.

We became step-siblings and began living under the same roof.

Although life is full of disappointments, such misfortune doesn't come knocking every day—it must be a trap set by a wicked God.

A trap set by God.

In other words, it's fate.

Although I've long since banished the days of my harmonious relationship with that man to the dustbin of my memory, I must regretfully admit that a few memories, like mold stains in a bathroom, still linger.

I remember it was between the second and third years of junior high school—during spring break.

That guy invited me to his house.

My dad isn't home today.

Because the man made the suggestion in a somewhat shy tone, I, in my foolishness, immediately thought:

finally come.

They've gone on dates, they've kissed, so what's next—it's perfectly natural for a modern junior high school girl to have these thoughts. It's not that I'm particularly prone to overthinking; I'm serious.

During that period, I often heard the girls in my class talking about those kinds of topics—this was because we girls had already begun to fight against those awful physiological phenomena. The distance between us and that concept was incomparable to that of those stinky boys who just looked at pictures online and yelled.

I am mentally prepared.

Finally, I was going to experience firsthand the knowledge I had only read about in books—with a mix of anticipation and anxiety of about three to seven, I successfully entered my boyfriend's room for the first time in my life.

They're even advancing.

Although I must admit I used a very silly analogy, I was indeed very prepared—needless to say, the night before I searched the internet for "things to know before your first experience" and even did some research on how to make sounds.

After carefully preparing my way into the man's room, my first step was to find a place to sit. The room was cluttered with books, and the only place I could sit was on the bed. There? Was I really supposed to sit there? Even so, as I timidly hesitated, the man casually said:

—Please sit down, don't be shy.

So, I ended up sitting on the bed, but then something amazing happened.

That man actually sat down next to me as if it were the most natural thing in the world.

I thought to myself:

--Huh...! More proactive than I expected...! He's usually so reserved!

Just how narrow-minded is this woman? She should just get hit by a truck and go to another world.

If it were me now, I would think that way, but unfortunately, back then I was too afraid of death to leave Earth and even started chatting with that guy.

I don't remember anything we talked about. My mind was completely preoccupied with when I would be pushed down, whether we would kiss first, and whether I was wearing the right underwear.

The man merely shifted his sitting position, and it sent my shoulders pounding. Even a slight touch of his little finger almost made me scream. Ten minutes, twenty minutes, thirty minutes passed in this pathetic display of virginity…

Then another hour, two hours, three hours passed—

Strange? Why hasn't it started yet?

Just as I started thinking that, the man finally spoke.

—It's so late already. So, you…

coming.

finally come.

I hope it won't hurt too much, I hope it won't be too scary, I hope everything goes smoothly...!

—It's about time to go home. I'll take you home.

......................................................

Huh?

—That, that…

—Although I'm very reluctant to see you go back, your family will worry if you go back too late.

And so, the man took me back to my apartment.

Does this mean they'll escort me to bed? Take me home and then directly to bed?

I had this doubt until the very last moment, but thinking about it carefully, my mother was at home. If he wanted to do that kind of thing, it would have been more appropriate to do it at his house.

The man waved to me casually in the apartment lobby and said this casually:

—I had a great day. See you another day!

I stared blankly as he left—and then I finally realized what was happening.

He invited me to his house, but that wasn't his real purpose at all.

She just wanted to chat with me in her own room.

I'm the only one who's eager to embrace this new stage of growth!

—Oh dear? Yui, why is your face so red? Do you have a cold?

After I got home, my mother came to check on me.

I couldn't even give a decent answer. I collapsed onto the bed, overwhelmed by shame, and wanted to roll around on the bed.

Then, about a year later...

Until the decisive turning point, nothing actually happened between me and that man.

◆

"Dad and Aunt Yu-ren said they'll be back a little late today."

Just as I had finally finished packing my moving boxes and was elegantly enjoying a classic mystery novel in my room, my stepson—I mean my stepson—came over and slowly reported the matter to me.

"...Oh, really. So what?"