The Fibonacci Cipher
"S-Sure, you'd despise me. Of course... you would. I'm s-sorry... I'm so sorry... Sorry for being such a trashy, vulgar teacher who does filthy things... Ungh...."
I could only slap my forehead.
No, that was a secret too, but this wasn't the kind of info I wanted to hear.
I'd hoped for the school's secrets or something deeply personal about her—serious stuff. Not someone else's sexual fantasies or weird fetish play.
Even if I learned this, I couldn't use it to convince a stranger. If some guy I'd just met blurted out, "I know you stayed at school until 1 a.m. to publicly masturbate in the classroom," no woman would stick around. Even if she didn't run, she'd slam her heart shut, assuming I was just trying to blackmail her into sex.
Aigoo, this woman...
"Hey... Su-hee. I really don't care. Whether you secretly got off in the classroom fantasizing about public masturbation or not, you're the one and only ally I have in this entire twisted world. I'm in no position to judge you."
"Wha...? R-Really?"
Her eyes widened at the unexpected response, looking up at me with a glimmer of joy in her pupils.
"Of course. Hell, with school duties like sex rotations, abortions... and even human sacrifices with dead fetuses, a fetish like that is nothing. Honestly, doing it alone in an empty classroom doesn't hurt anyone. I get it. Probably just blowing off work stress, right?"
"Ugh...! Y-Yes! S-Stress! To vent stress...! Th-That's why!!"
"Shh!"
As her face flushed and her voice grew louder, I pushed her back against the bookshelf, trapping her against my chest and gently placing my hand over her mouth.
"Eek... S-Suddenly like this..."
"Huh? I just said don't shout."
"Gasp..."
Not as bad as Kang Jia, but Su-hee was no ordinary woman either.
"...I get it. For real. So don't worry. But..."
"B-But...?"
"Sigh... What I really wanted wasn't that. From a stranger, I needed a 'trustworthy' secret—something only you know, like a school secret or your childhood diary entry."
"Guh!?"
She trembled violently, finally covering her face completely with both hands.
Only now realizing how idiotic her confession was, huh?
"Ugh... Aaaah! What the hell did I...!"
No time to watch her flail in self-loathing.
"Su-hee, it's fine. I don't say empty words. Forget that—tell me the real info I need. Something special enough to make you trust a mysterious guy you just met."
I lightly patted her shoulder, and she seemed to snap out of it.
"Y-Yes... Haaah... Special info, right..."
Her eyes stared into space, searching her memory.
"Hmm... Ah! There's one thing no one knows—not even my parents. No long explanation needed. A short code only I know."
"A code?"
"...It's kinda embarrassing to share, but... 'Su090421'. Remember that."
"Su090421? What's that?"
"It's... the password for my first messenger account in middle school."
A messenger password?
"Hm... A password from over ten years ago would be hard for anyone to guess, but what if someone hacked it? People love fitting puzzles, so if you met 'next round me' and shared this, she might suspect hacking or something."
"Maybe, but... that date's super special."
"Special how?"
What could it be? The day she fell in first love? Or something with that dog Coco she mentioned?
"Yeah... I don't know what I was thinking, but that date... is the day I got my first period."
"Huh?"
Using your menarche date as a password? I'd never heard of anything so bizarre. For a guy, it'd be like using the day you first sprouted pubes or had your first wet dream.
As I scrunched my brows in utter confusion, Su-hee frantically explained.
"I-I don't know either! I was in middle school, okay? It meant nothing—just a coincidence that my first period hit the same day I signed up for messenger, and they said use an easy-to-remember date, so I did it without thinking!"
This was the first time I'd seen Su-hee ramble like this. Even facing monsters threatening her life, she'd stayed cool and made the best calls.
"Uh... yeah, sure. No one would know that. Even if hacked, using your period date as a password... yeah."
"R-Right? Heh... hoho..."
Awkward laugh as she slipped out of my arms.
"Th-Then I'll go dig up more!"
I'd expected first love stories or Coco memories at best, but I got mind-blowing info instead.
A woman I'd just met's first period date. Plus her weird fetish...
Info I never needed or wanted, now burned into my brain forever.
Dizzying.
I shoved the little mishap with Su-hee aside and turned back to the bookshelves.
"Haa..."
Looking at the books, they still made my head spin.
Just like Su-hee's code I'd just learned.
"...A code?"
A code...
Code...!
A spark like lightning flashed through my mind.
Finally, I understood why this 'Ha' row shelf alone gave me vertigo.
The library's shelves were massive seven-tier units, big enough for two grown men side by side.
Books should be sorted alphabetically by title: ga-na-da-ra...
But the 'Ha' row was a jumbled mess.
Why? It wasn't the titles—it was the library barcode numbers on the covers.
They started normal:
Ha-0, Ha-1, Ha-1, Ha-2, Ha-3...
Two Ha-1s was odd, but possible. Still sequential: 1,2,3.
But as my eyes moved right, the order broke:
...Ha-34, Ha-89, Ha-144.
These numbers must form a pattern.
My brain heated up, gears turning. Other shelves were normal—this one alone was off. What rule governed it?
"Prime numbers?"
No, not primes—34 and 144 aren't.
Then...
"Ah!"
Not random—a distinct sequence.
How had I missed something so simple?
Spotting it, the pattern visualized: graphs spiraling, numbers marching to infinity. Recursive sum of previous two...
The golden spiral whirled before my eyes, its center like a peephole thrusting forward.
Beyond the "divine ratio" hole, the village boundary's severed space flickered vaguely. Something black reached from there, linking to my mind—a sickening sensation.
"Ugh."
I shook my head to dispel the hallucination.
Anyway, I'd cracked it. The book numbers meant:
Fibonacci sequence...
Deliberately arranged. This entire shelf was a cipher container.
Who'd bother sorting by Fibonacci if not intentional? Lazy folks dump randomly.
Thrill of discovery hit, but doubt crept in: Why did I—no math whiz—recall infinite Fibonacci terms? And that village hallucination...
Did that prior experience alter my brain?
"Hoo..."
I pressed my temples, calming my number-flooded mind. Focus on the puzzle now.
Solve step by step—we'd reach the answer.
I scanned from top left:
"...Ha-8, Ha-55, Ha-233 are missing."
All others followed Fibonacci—except slots 8, 55, 233.
"8, 55, 233..."
I repeated them endlessly.
Not dates—too spread out.
Not coordinates—too short.
No complex cipher—too simple.
"Simple..."
Yes. Overcomplicating was pointless.
Not a hard secret puzzle—designed for attentive eyes. A simple trick.
Clear my head. Apply the numbers plainly.
A sequence is numbers in fixed order.
Fixed order. Order.
"Ah..!"
I rushed to the 'Sa, A, Ja' row shelves.
Applying 8, 55, 233 in sequence made their meaning crystal clear.