PDS Chapter 1.5

Yeon Suho carefully placed my toothbrush in a long ziplock bag he’d found lying in the locker.

Something about it felt oddly unsettling and kept nagging at me, but his sheer confidence left me too overwhelmed that I just let it slide without saying anything.

‘Anyway… that’s not important right now.’

It was time to make some real progress in the game.

“Let’s go.”

We entered the next classroom, Class 3-3. Just like my classroom, the lights were off, making it dim, but otherwise, it looked like a normal classroom.

However, there was something different about this place than Class 2-3.

It was set up as if in the middle of a class.

“Wh-What is this…?”

There wasn’t a single person inside. There was no teacher holding a piece of chalk, no students solving problems at their desks or dozing off.

Yet, every textbook was open to the same page, and the desks and chairs were neatly arranged with even spacing, as if occupied, creating an eerie, unsettling atmosphere.

When I first came in here and saw this scene, I almost passed out. Now, I was prepared for it, so it wasn’t as shocking.

“Class is in session, Yeon Suho. Open your textbook and take your seat.”

I tried to lighten the mood with a joke. However, Yeon Suho just stared at me with a bewildered expression, and I suddenly felt awkward, which only made the atmosphere even weirder.

“Ahem.”

I cleared my throat and walked to the front of the classroom, composing myself.

A complex equation was written in the middle of the blackboard, and a box sat on the teacher’s desk.

It was just one line, but it was a linear partial differential equation, something you wouldn’t normally see in a high school math class.

And the box—it was square, about the size of a large textbook, with a hinged lid that could be opened from one side.

This was the puzzle provided by Class 3-3’s classroom.

Yeon Suho looked at the box curiously and reached out to touch the lid.

“What’s in this box?” 

“Hey, don’t touch it! It might be dangerous.”

I immediately warned him not to open it carelessly—doing so would be a disaster. That box was the trigger for yet another instant death ending.

If you simply opened the box, poisonous gas would leak out, killing you on the spot. I knew this because I’d made that mistake in one of my earlier playthroughs. I’d knocked on it, shaken it, nothing seemed to be inside, so I opened it. And died.

‘At least dying that time taught me something useful.’

The bad ending title was <Poison of the Microscopic World>.

This was a perfect example of how even the ending titles could be clues. “Microscopic world” referred to the realm governed by quantum mechanics, and quantum mechanics was one of the fundamental theories of physics.

I spent a long time searching through books related to those keywords in the library before I finally figured out what the equation on the blackboard was.

“That’s the Schrödinger equation, a fundamental equation in wave mechanics.”

As I pointed at the blackboard and spoke, Yeon Suho nodded, looking at me with the wide-eyed enthusiasm of a keen student. Good reaction.

Honestly, I didn’t fully understand what wave mechanics or matrix mechanics were, even after looking them up. I was an engineering major, not a physics major, and it had been a long time since I’d last touched any math after graduating.

‘But at least I knew the theory associated with the name Schrödinger.’

Schrödinger’s cat. A thought experiment devised by the physicist named Schrödinger to illustrate the incompleteness of quantum mechanics.

The experiment went like this: 

A cat is placed in a sealed box along with a radioactive substance that has a 50% chance of decaying within an hour, a Geiger counter to detect the radiation, a vial of poison, and a hammer. If the radioactive substance decays, the Geiger counter detects it, triggering the hammer to fall and break the vial, releasing the poison.

After an hour, is the cat alive or dead?

The answer is, ‘Until the box is opened, the cat exists in a superposition of both alive and dead states.’ But I didn’t need to know all those details. With these kinds of puzzles, it was all about intuition and keywords.

At first, I’d thought I actually had to solve the equation on the blackboard, so I ran around looking for values to plug in, wracking my brain trying to multiply and divide and do all sorts of crazy calculations.

I eventually gave up, thinking it was a problem that was impossible to solve. But then, after teaming up with Yeon Suho and checking the list of items he had, it suddenly clicked.

“Don’t open the box. Just stand in front of it. And you know that cat treat you have? Open it.”

Yeon Suho, looking puzzled, obediently took out the cat treat and tore open the corner of the pouch as I instructed.

Would this work? It had to. I didn’t want to waste an item and lose my companion’s trust for nothing.

As I watched the box with a mixture of hope and anxiety, I heard a faint click. Something moved inside, and the lid of the box rattled.

“……!”

After rattling a few times, a small, fluffy front paw reached out from inside the box.

What followed was a pitch-black cat, its entire body as dark as a shadow, with only its yellow eyes standing out.

“Yes!”

The box that was supposed to be filled with poisonous gas had, miraculously, produced a very calm and polite-looking cat. 

Nice to meet you, kitty. 

Seeing this little furball the moment I finally solved the part I’d half given up on looked even more precious and adorable.

“It’s eating well.”

The cat eagerly lapped up the treat from Yeon Suho’s hand. Yeon Suho smiled softly, slowly squeezing the pouch so the cat could eat comfortably.

It was a rare moment of peace in this terrifying game.

“Looks like it’s done…”

Having finished the treat, the cat licked its paws, cleaned its face, and then hopped off the teacher’s desk. Then, it sauntered past the desks and out the open classroom door.

As I watched it go, wondering if I should follow it, Yeon Suho spoke,

“I think there’s something else in the box, senior.”

“Huh?”

At those words, I quickly looked inside the box.

Left behind in the box that had contained either poison or a cat was a card with a picture on it.

Ⅵ. THE LOVERS.

A naked man and woman stood in a meadow at the foot of a mountain. Behind the woman was a serpent coiled around a fruit tree, and behind the man, a barren tree was engulfed in flames. An angel, with her back to the radiant sun, looked down on them from above the clouds.

“A tarot card?”

A single tarot card. That’s what I found inside the box.

I turned around with the card in my hand, but the cat was already gone.

“…….”

Well, I guess it was fine to let it go. I didn’t know what it meant, but the tarot card seemed to be my reward for solving the puzzle.

“I’m sure it’ll be useful for something.”

I carefully tucked the card into the inner pocket of my bag. Then, I left the classroom with Yeon Suho.

There was nothing else to do on the second floor of the main building for now. Our next destination was the annex, where most of the specialized classrooms were located.