The Chemical Engineering Department Has a Scary Younger Sister

The four characters written on the front gate—Hogukyoram—I didn't know their exact meaning, but I guessed it was something like "the cradle that protects the nation."

It was a phrase I'd heard often enough that it felt familiar to my ears.

The front gate of the Nonsan Army Training Center was bustling from lunchtime onward.

Countless vehicles lined up in a long queue while instructors holding red fluorescent batons directed traffic in perfect formation and conducted quick inspections.

The instructors visible through the windows all wore the same blank expressions.

Given that this scene repeated every month—or even every week—it was only natural.

After waiting for quite a while, our turn finally came.

Mom slowly pressed the accelerator after the inspection, and the car slid smoothly into the training center grounds.

The moment we passed through the front gate, my heart seemed to skip a beat for no reason.

Sitting in the back seat and staring blankly out the window, I let out a deep sigh without realizing it.

It was a sigh half filled with resignation and half with tension—So it's finally happening.

Just then, my younger sister, who had been sitting right next to me, suddenly threw her arms around my neck.

"Oppa, don't leave me behind… sob sob…"

I flinched at the damp sensation against the back of my neck.

Wondering if she was actually crying, I turned my head—only to see Jiheon with real tears welling up in her eyes.

What the—? Was she seriously crying?

"Why do you look more upset than the guy who's actually enlisting?"

"Of course I do…!"

Jiheon jerked her head up.

Her tear-filled eyes sparkled moistly in the sunlight.

"My future husband is going to such a dangerous place… My delicate, feminine, cute, sexy, seductive, lovely older brother is heading into an army full of wolves! Of course I'm worried!"

Using six adjectives in a single sentence would have made any Korean teacher faint.

The fact that every single one of them was describing me only made it worse.

"More than anything, the thought of not being able to smell your scent for a year and a half… I can't even imagine it!"

I really wished she'd stop saying things like that.

Thinking that to myself, I peeled my sister off me—she was clinging like a leech.

She was stronger than I expected, so it took some effort, but I eventually succeeded.

Grabbing her by both shoulders and keeping a safe distance, I spoke as calmly and slowly as possible.

"First."

I held up one finger.

"We're siblings. Legally, marriage is forbidden. So I'm not your husband."

"……"

"Second."

I raised another finger.

"You keep teasing me by saying I look like a girl. You know that's my complex, right? I've told you countless times to stop mentioning it. And I'm a guy too—what's wrong with going somewhere full of other guys?"

"……"

"Third."

Three fingers were now raised.

"From now on, stop taking my clothes out of the laundry basket to sniff them, stealing my underwear to wear, or sneaking into my bed in just your underwear to bury your face in my pillow and smell it. You're a high school senior now—it's time to quit."

Listing them out, it was quite a long list.

Even as I spoke, I bit my lip hard, thinking, Is this really something siblings should be saying to each other?

Jiheon looked up at me with slightly teary eyes.

Just as a pang of guilt started to creep in, she lunged forward and hugged me again.

"But still!"

I tried to pull her off, then gave up out of sheer annoyance.

After all, I wouldn't see her for a year and a half anyway.

"Smelling your scent is my only joy in life!"

"Calling that your 'joy in life'… You really do live a wholesome, dopamine-free existence, don't you? Why don't you try drinking or smoking instead?"

In an instant, Jiheon's gaze turned ice-cold.

Her sharp, piercing stare was genuinely intimidating.

"How could you suggest that a third-year high school girl start drinking and smoking?"

Her voice was laced with thorns.

"That's so unhealthy!"

Stealing and sniffing my worn underwear or rubbing herself against my blanket in my bed seemed far less wholesome, but I ‍‍‌‌⁠​​⁠‌​​‍​​‍​‌​⁠‍‌‍⁠⁠‌⁠‌‍‌‍‌‌‌‍⁠​‌​‌​‌‍‌‌‌⁠‍​​‌‍⁠‌‌⁠⁠swallowed those words without saying them.

While I was struggling to detach my leech-like sister, the old Sonata Mom was driving came to a gentle stop.

The car was old, so the brakes let out a squeak every time she pressed them.

"Kids, stop with the affection and get out already."

Mom's eyes appeared in the rearview mirror.

She looked unfazed, as if she'd grown used to the kind of sibling conversation that would make anyone else faint.

"It's already 12:50. You said you had to be there by 1."

"That's because you overslept and made us late, Mom."

It was a fair point. We'd planned to leave at 7 a.m., but Mom had turned off her alarm and gone back to sleep, so we didn't leave until after 9.

I'd been anxious the entire drive to Nonsan.

But Mom simply ignored my words and got out of the car.

Our family really did seem to carry a selective hearing gene.

We followed her out. The moment the door opened, the chilly March air stabbed into my lungs.

The sky was overcast and gray, and somewhere in the distance, a loudspeaker droned on.

Far away, the parade ground came into view. Young men with buzz cuts and expressions similar to mine stood lined up—poor souls who'd been forcibly conscripted.

Every single one of them had a dazed look in their eyes. I was probably making the same face.

As I started walking toward them, something slithered into my hand.

Turning my head, I saw my sister trying to sneakily interlock her fingers with my right ‍‍‌‌⁠​​⁠‌​​‍​​‍​‌​⁠‍‌‍⁠⁠‌⁠‌‍‌‍‌‌‌‍⁠​‌​‌​‌‍‌‌‌⁠‍​​‌‍⁠‌‌⁠⁠hand.

"……Hey."

I shook her hand off.

Jiheon looked disappointed but didn't give up.

Again and again, I fended off her persistent attempts to grab my hand while walking quickly.

To anyone watching, it probably looked like some kind of couple's game.

I really hoped no one was looking.

Only the enlistees were allowed onto the parade ground.

Families gathered on the stands beside the command platform to see off the poor souls being dragged into the training center.

Parents waving their hands, girlfriends sitting quietly and watching, friends standing around laughing like it was funny—everyone was saying their goodbyes in their own way.

I walked in formation under the instructors' sharp commands.

Staring at the buzzed head of the person in front of me, I suddenly felt uneasy and glanced back.

On the stands, my sister was sobbing loudly.

She kept dabbing at her tears with a handkerchief while staring in my direction.

Her blonde hair, tied in a side ponytail, swayed in the wind.

Even from afar, I could see how red and swollen her eyes were.

……What the hell.

Normally she was annoying and sometimes even creepy, but seeing her cry this much for me… I felt a tiny, very tiny bit moved.

After all, we were siblings. It made sense to cry when you wouldn't see each other for a year and a half.

Even if her obsession was a bit extreme, she still cared—

Just as that thought crossed my mind, a familiar female voice rang out loudly from the stands right before I left the parade ground.

"Oppa!"

Her voice stood out clearly in the quiet stands.

"Until the completion ceremony, don't wash your underwear! You have to come out still wearing them!"

……

…………

For a moment, everything seemed to go silent. Or at least, it felt that way.

I heard the enlistee next to me snicker, "What the hell was that?"

My ears turned bright red.

I could feel the heat rising to my face. Blushing when embarrassed was a habit I'd had since childhood.

It was my fatal weakness—I couldn't hide it no matter how hard I tried.

Please. Please let no one realize that girl is my sister.

Doing my best to act like nothing happened, I lowered my head deeply to hide my reddened ears.

I wanted to cover them with my hands, but that would only make people more suspicious, so I held back.

Moved? Yeah, right.

As expected, my younger sister—who was obsessively attached to me—was terrifying.

The fact that I'd be separated from her for a year and a half suddenly didn't seem so bad.

The hardest part of training camp wasn't the training itself.

Drill formations, exhausting marches, and even the surprisingly scary live-fire exercises were tough, but I could endure them somehow.

Group living wasn't as bad as I'd expected either.

Dozens of men sleeping, eating, and showering in the same barracks with zero privacy—but I adapted.

The ‍‍‌‌⁠​​⁠‌​​‍​​‍​‌​⁠‍‌‍⁠⁠‌⁠‌‍‌‍‌‌‌‍⁠​‌​‌​‌‍‌‌‌⁠‍​​‌‍⁠‌‌⁠⁠food wasn't a problem. People complained it tasted bad, but it wasn't so bad I couldn't eat it.

What was truly difficult was…

Not having access to my phone or the internet.

It didn't seem like much, but it was surprisingly serious.

My hand would instinctively reach for my phone before bed to watch videos, and I'd unconsciously pat my pocket whenever I got bored.

Of course, there was nothing there.

I realized just how real digital withdrawal could be.

But even that had its upsides.

Since I couldn't play games or browse communities, I naturally spent more time talking with my fellow trainees.

It felt awkward and uncomfortable at first, but after a few days, it became surprisingly fun.

From pointless chatter to serious heart-to-heart talks, I found myself opening up without realizing it.

Another thing that was almost as hard as not having internet was not being able to masturbate.

I usually needed to do it three times a day to feel satisfied, so going a whole month without it was unimaginably difficult.

But sneaking off to the bathroom alone while the others were asleep didn't appeal to me either. I'd rather just endure the blue balls.

Amid this frustration, I discovered an unexpected pleasure in training camp life.

Seohan University—one of the top five most prestigious universities in Korea.

And on top of that, the engineering department. I was a third-year student in Chemical Engineering and Biotechnology.

Normally, I didn't think much of it. After retaking the entrance exam three times just to get in, the feeling of relief that I'd finally made it outweighed any pride.

On campus, there were plenty of people more impressive than me, and my grades were only average, so I didn't stand out.

But the military was different.

"Hey, what university do you go to?"

It was rude to ask like that—especially since I could've been a high school graduate.

But I'd been waiting for this moment for a long time.

Someone to make me say the name of my university myself. So I answered with a casual expression.

"I'm on leave from Seohan University. Chemical Engineering and Biotechnology."

The barracks fell silent for a moment.

"……Seohan University?"

"Whoa, that's insane. First time I've seen someone from there."

The way my fellow trainees looked at me changed.

A mix of respect and curiosity—like they were observing a rare animal.

"It's me."

As it turned out, I had the highest level of education in our regiment.

There were no graduates from the so-called SKY universities, and only a handful from top-tier Seoul universities.

Most came from regional universities, junior colleges, or were high school graduates.

Suddenly, more people started asking me questions.

Even trivial opinions gained credibility when prefixed with "This guy from Seohan University said…"

Even the instructors spoke to me with a slightly different tone.

……This feeling.

It wasn't bad.

Actually, if I was being honest, it felt pretty good.

So, as a proud Seohan University student, I tried to speak eloquently and acted sociable, pretending to be an outgoing person.

Maybe I was unexpectedly talented at it—despite being the type who was usually shy and introverted.

With my usual dopamine sources cut off, I was seeking it through human relationships instead. Human adaptability really was amazing.

And then there was one more thing.

In a place where every source of dopamine was strictly controlled, there was still one thing I could look forward to.

Internet letter time.

Every evening, the instructor would distribute the internet letters that had arrived that day.

Letters from ‍‍‌‌⁠​​⁠‌​​‍​​‍​‌​⁠‍‌‍⁠⁠‌⁠‌‍‌‍‌‌‌‍⁠​‌​‌​‌‍‌‌‌⁠‍​​‌‍⁠‌‌⁠⁠parents, girlfriends, friends—everyone received one or two and smiled.

I received ten letters every single day. All from my younger sister.

Jiheon sent me long letters without fail, every single day.

Not just one—ten of them. Probably because there was a character limit per letter, so she split them up.

The content was pretty much what you'd expect: "I miss you, Oppa," "Please stay healthy, Oppa," "I love you, Oppa"—stretched out over several A4 pages.

The problem was the instructor handing them out.

"Trainee number 103."

"Trainee number 103, Seo Chaewon!"

I jumped up and answered.

"You've got another ten internet letters full of love again."

The instructor grinned as he waved the bundle of letters.

"From your girlfriend, no less. I'm jealous, really jealous."

All eyes in the barracks turned to me at once.

Whispers of "His girlfriend must be something else," "Ten letters a day? How much does she like him?" and "I'm so jealous" filled the air.

She's actually my biological sister.

……Not that I could ever say that out loud, even if I died and came back to life.

"Th-thank you!"

My voice trembled slightly.

I ran up to the instructor and took the letters.

"Is she pretty?"

The instructor asked leisurely.

It was clearly half curiosity, half teasing.

"N-no, she's not that pretty!"

The answer slipped out reflexively.

In reality, my sister was quite beautiful.

Actually, even as her older brother, I had to admit she was very pretty.

She'd trained as an idol trainee for about a year in middle school—she had the looks for it.

She eventually quit because it didn't suit her, but her face alone would've been enough to make it in that industry.

Still, I had a feeling that saying she was pretty would cause serious trouble.

"Really?"

The instructor tilted his head, looking puzzled.

"But sending ten letters every day… she must really like you. Treat her well when you get discharged."

"……Yes."

Not knowing what else to say, I just lowered my head.

As I walked back to my seat, one of my fellow trainees spoke from behind me.

"Hey, Seo Chaewon. Your girlfriend's really something. Ten letters a day—doesn't her hand hurt?"

"……Yeah, right."

I brushed it off vaguely and opened one of the letters.

I quietly folded the letter.

Yeah… it was probably better for my mental health not to read them.