There are only three boys at this school.

Me, a senior, and the physics teacher. Every first-year student is a girl.

The school has about 300 students, so boys make up only 1% of the total.

The reason for this is a deadly virus that suddenly appeared three years ago, and it only infected men.

It’s called the “Adam Virus.”

Once they caught it, there was no saving them. It killed them within a week. On top of that, it spread to anyone within a one-kilometer radius.

Because of it, 99% of men around the world died.

That’s right, 99%.

People thought all men would die, but 1% were born with natural immunity to the virus.

I’m one of the lucky ones with that immunity. That’s why I’m here today.

But honestly, I’m not sure if being lucky feels good at all.

“Ah, Saotome-kun!”

“You look so cool today!”

“Your hair’s messy, so cute~”

Before the Adam Virus, I wasn’t really noticed in class.

I’m about 170 cm tall, and my face is average. There was nothing special. I'm just another guy they’d see in any class.

Now, I’m basically the school’s idol.

No, idol is too soft a word. I’m treated like a rare creature on the brink of extinction.

Even in class, the girls in the back stare at me painfully.

During breaks, someone always talks to me. “Let’s eat together,” or “Let’s study in the library.”

If I say no, they get obviously disappointed. If I say yes, other girls get jealous. There’s no winning here.

The only place I can feel relaxed is at home.

“Ah, welcome home, big brother.”

At the door, my stepsister Ruka greets me.

She’s my dad’s new wife’s daughter and started attending the same high school as me this year.

Long silver hair, clear eyes, and a slender body. She’s a quarter Nordic and really beautiful.

Unlike other girls, she doesn’t treat me differently. She acts like nothing has changed, just a normal sister. That’s what makes me feel safe and at ease.

“Hi, Ruka.”

The world has changed a lot in the past three years.

With so few men left, society, schools, and relationships have all changed.

But at home, everything feels normal. That’s something I’m really grateful for.

Still, sometimes I can’t help but wonder.

Has Ruka really stayed the same?

Lately, it feels like she’s looking at me longer, talking to me more often…

No, it’s probably just my imagination. I’m overthinking things.

I was thinking about this while rinsing my mouth in the bathroom.

Prologue