“...What is this place?”

Splish, splash.

Dog-paddling through the water in the tank, Ziel reached the edge, pulled himself up with a grunt, and shook his body to fling off the water droplets. Then, he took another good look around.

The scene was bizarre.

He had no idea how to describe it. He had never seen anything remotely similar before. The artificial blue lights at the bottom of the tank illuminated the surroundings, but even that shade of blue felt unfamiliar.

The space was enormous. Even just what he could see was wider than an Eastern dojo, meaning the entire structure must be larger than the ancient ruins he had just been exploring.

A building.

Yes—this was a building.

Looking up, he saw that the ceiling was open three stories high. Running along the walls at what would be the height of a first-floor and second-floor roof were metal catwalks. They were wide enough for a person to walk on without trouble, but compared to the scale of the building, they seemed absurdly small.

Beyond the catwalks, there were doors.

Which meant there was definitely more space beyond.

“...And this floor, what’s up with it?”

It was too smooth. He tapped it with the toe of his shoe.

The floors of the ruins he had been exploring were smoother than the jungle paths, but this was on another level. Completely seamless, with a texture that didn’t feel natural at all. The surface felt soft under his feet, and he wasn’t even sure if it was made of natural materials. He couldn’t tell.

“...This doesn’t feel like just a water tank.”

This place was clearly different from the ruins he had seen before.

Not only that, but it was more advanced, more refined.

What exactly was this place? He had no way of figuring it out with his own knowledge and reasoning, so instead, he remembered—he had made it here safely.

He had to pull the rope three times to let them know.

So he tugged on it—

And felt nothing.

“...”

Just to be sure, he pulled harder.

The severed rope slid back to him, perfectly cleanly.

“...”

Klaha’s face had gone pale.

She gripped the severed rope tightly in both hands.

“Uh, um… I-I’m sorry…”

“It can’t be helped. Ziel is just that kind of person.”

“No, no! It’s okay, Klaha! It’s okay—Ziel, you see—he can breathe through gills!”

“Can he?”

“P-please just go with it…!”

It had all happened in an instant.

From the moment Ziel leaped into the waterfall, the rope had shot out with terrifying speed. Lililia had been quick to use holy magic to protect Klaha’s hands from being burned by friction. Even so, the speed was enough that one might think it could start a fire.

Just how many days would it take Ziel to run from one end of the continent to the other if he went all out? It was an absurd thought, yet impossible to ignore.

Klaha replayed the moment in her mind.

The rope had gone taut—snapping her body forward. She had nearly fallen out of the boat. Lililia had caught her, keeping her balanced.

She had tried to signal him to stop. She had held on tightly, determined not to let go.

And then—

Snap.

More effortlessly than a single strand of damaged hair breaking, the rope went limp.

What could she have done?

Klaha knew she would be thinking about this for the rest of the day.

“I don’t think it’s that big of a deal,” Lililia said, surprisingly unconcerned.

“Huh…?”

“I mean, Ziel went to find the source of the water, right? That means he’s been following the flow. If he’s consistent about that, then—”

She smiled.

“—if we follow the water’s flow, we’ll find out where he went. Sure, there’s a distance problem, so it might take a while to meet up, but it’s not like we’ll be separated forever.”

Eunice nodded vigorously beside her.

Klaha understood they were trying to reassure her. So she forced herself to shake off her doubts and said—

“Right—”

But just then—

Plop.

A small sound rippled through the water.

What was that?

Klaha instinctively reached for her sword and stepped in front of Lililia and Eunice, shielding them. But she soon realized what it was.

A severed piece of rope was floating.

Not the one they had.

“Oh?”

Lililia reached out, scooping it up with her long arms. She stared at it for a moment, then smiled.

“He says he’s fine.”

She held it out for them to see.

Carved into the rope were the words—

“Made it safely.”

It had seemed like a good idea.

But the problem was that the drainage didn’t necessarily have just one exit.

Also, the issue of what to write with and what to write on had made his handwriting messier than usual.

“Well, anyway.”

Right now, Ziel didn’t have the luxury of dwelling on that.

Looking up again, his eyes had adjusted to the light. He could make out more than just the catwalks. Blurry shapes were beginning to take form.

He wanted to see more.

He could take the stairs up, but this wasn’t a city. There was no reason to follow the normal paths.

“Alright.”

With a simple jump, he soared to the height of the second floor—

Landing effortlessly on the highest catwalk in sight.

The immediate concern, Ziel thought, was regrouping. If his message had made it, those three would figure something out. But he had no way to confirm that. Since there was no guarantee he could return the way he came, it made sense to look for any clues in the meantime—without getting too lost.

As he took his first step, the sole of his shoe made a clank against the floor.

Unlike the unknown material of the floor beside the water tank, this surface was familiar. Metal. A lightweight kind, it seemed—but sturdy enough not to bend under his weight.

That alone spoke of remarkable craftsmanship.

And the more he thought about it—the stranger it seemed.

This space was directly connected to the prehistoric ruins. If it wasn’t a secret underground area built by some rare modern person with both courage and the exceptional skill required to construct within a semi-labyrinth, then that meant this place was part of the prehistoric ruins.

And yet—why?

“...It doesn’t look like it’s about to break down.”

It was established thousands of years ago.

In the middle of the jungle, so close to the water’s edge, could this light metal really have maintained its shape for such a long time without rusting or deteriorating?

Suddenly, Ziel shuddered.

The reason was twofold. First, because a feeling crept over him—one that sent chills down his spine, somewhere between fear and curiosity—whispering that perhaps he was in a place beyond his comprehension, witnessing something truly extraordinary.

The second reason—

“—Air conditioning?”

Impossible, Ziel thought.

But as he resumed walking and pressed his hand against the pipe running along the wall near the service entrance, he was certain.

Cold.

It was unmistakably colder than any object should be in the summer.

Since he had swum up from an underground space, it wasn’t completely unreasonable to assume the temperature here might be lower. However, this felt eerily similar to the cooling magic Eunice and the others had used at the research facility where he had spent the summer. He couldn’t shake the feeling that magic was involved.

“……”

It was nothing more than a hunch—no logical basis, no real evidence.

And yet, Ziel thought—

Wasn’t this the very place that had caused the tremor?

“Just a little more…”

He murmured to himself, knowing exactly why he had done so.

He was shaken.

He had traveled the world and seen countless unbelievable sights.

But this—this was the first time he had witnessed such an extraordinary sight in a space so unmistakably shaped by human hands.

The only sound was the flow of water.

Where was the water in that tank being pumped from? Pondering that question, Ziel walked on, his footsteps echoing loudly.

Before the door.

Stopping right in front of whatever lay beyond.

“This is metal too.”

He tapped his knuckle against it, producing a firm, hollow sound.

It seemed quite thick. The artificial lighting wasn’t particularly bright, so he crouched slightly to examine it carefully. The design was unfamiliar. He couldn’t even determine where the hinges were.

“…Won’t open, huh?”

The ship’s wheel-like object in the center looked like it might be a door handle, but gripping it revealed that it wouldn’t push, pull, or slide. Turning it, as one would a ship’s wheel, did nothing. Even the sideways sliding mechanism used in the Eastern countries proved ineffective. It wasn’t simply jammed—it was deliberately sealed.

For a brief moment, he considered cutting it down.

But he quickly dismissed the thought. This was a valuable ruin; he couldn’t bring himself to damage it carelessly.

“…Hm?”

So, if possible, he would find another way.

As he examined his surroundings more closely, something caught his eye.

Next to the door.

A small box was mounted on the wall.

He had no real reason for it. He wasn’t expecting much. It was just a continuation of his previous attempts at interacting with the door. He reached out and lightly pulled on it.

Click.

To his utter confusion, it opened.

“What…?”

He was startled by his own actions. Should he have opened it? He glanced around, but since he was alone, there was no one to reprimand him. He looked back at the inside of the box.

There were several small drawings.

Ziel found it difficult to describe. They were abstract—symbols of some kind. Most of them were incomprehensible to him, but one in particular stood out.

A drawing that seemed to depict a flow of some kind.

Beside it, an identical drawing—but marked with a large X.

He hadn’t thought much of it.

It just seemed related to the water channels. Acting on instinct, he reached out, intending to confirm his suspicions.

But then—

“Huh?”

His finger easily pressed into the drawing with a soft click.

A deep, mechanical shift echoed through the space.

Startled, Ziel quickly withdrew his hand. What had he just done? It was ridiculous to panic after pressing it himself, but he hadn’t meant to! He glanced around. He didn’t notice anything immediately, but after a short moment, the change became apparent.

Below.

The water level in the tank was steadily dropping.

“……”

On one hand, he felt he had accomplished something significant. On the other, a creeping sense of dread filled him. He had undeniably manipulated the ruins. Under the current circumstances—where his primary objective was to regroup with the others—this might have been the best possible outcome.

However—

“…Is this really okay…?”

Was it really just that? He had no way of knowing.

The visible effect was only the lowering water level, but what about the unseen consequences? What if, outside these ruins, something catastrophic was happening? What if, instead of just a tremor, this drainage system was flooding the entire jungle? He didn’t want to believe that such a disaster could be triggered so easily—but throughout history, it was often the unseen that caused the greatest unease. If there was any way to gather more information—he just needed to listen carefully—

Clang.

…A sound echoed in the distance.

“!”

Ziel’s shoulders jolted in alarm—not because the sound had come from the tank, but from the opposite direction.

Deeper within the ruins.

From a place no one had stepped foot in.

Clang.

Clang, clang, clang.

He noticed another sound mixed in—something moving across the soft floor. A rhythmic, measured motion, like the ticking of a clock.

Something approaching.

“——”

Ziel held his breath.

Moving cautiously to avoid making a sound, he placed a hand on his sword’s hilt. Stepping back slightly from the door, he positioned himself on the elevated walkway.

Clang. A noise, closer now.

Footsteps followed.

Four seconds of silence.

Then, the final door emitted a deep clang as the ship’s wheel began to spin.

The door lifted.

The door opened.

And there—

A doll with crimson eyes.

Staring at him with its vivid red gaze.