It was a simple principle that let them figure out their destination.

The sound had been echoing from that direction all along.

First, the waterfall that Klaha had been facing in the underground waterway vanished.

They had noticed the water flow increasing along the way, but now it had completely stopped, leaving the drainage pipes empty. It hadn’t been long since they received the message written on the piece of rope, so they were almost certain—Ziel had accomplished something.

Then, the sound began to resonate. It was an immense noise. The water's surface rippled, and Klaha seriously worried that if it escalated any further, the old waterway might collapse.

Since there was sound, all they had to do was follow it to its source.

Klaha spoke. Something might have happened over there. Since she could guide them, why not go meet up?

The other two readily agreed. Then, Eunice suggested that if they knew where they were going, it might be better to use magic to get there quickly. It was a reasonable idea, so Klaha nodded. "Yes." Lililia then added, "In that case, maybe I should put up a wall to keep us from getting wet—something round."

"Huh?"

Klaha didn’t quite understand and couldn’t nod in agreement.

"Sounds good."

Eunice seemed to understand and nodded.

What followed was probably a very precious experience, one that they could recall with a smile for a lifetime. But in the moment, they were so focused that they barely remembered any of it.

There was a magic spell that made water surge backward through the drainage pipe at an incredible speed.

Encased in a round barrier of holy magic, the three of them were propelled forward at high speed.

Momentum carried them the rest of the way.

"This place is incredible…"

The sheer spectacle of it made Klaha forget the momentum that had carried them there.

The room that once held a water tank now stood empty, illuminated by Eunice’s blue magic light. Klaha’s gaze traveled from one wall to the ceiling, then to the opposite wall.

It felt like a dream.

But surely, it wasn’t. The sight before them exceeded the limits of their imagination too much to be something from a dream.

For now, the situation had settled.

The mysterious entity that Ziel had been confronting, the echoing sounds—Eunice had put a stop to them the moment they arrived.

Now, there was only silence. In the distance, beyond the drainage pipe, they could faintly hear the sound of flowing water.

"I have a lot of thoughts about this," Eunice began.

"But first, we should decide on a general course of action."

"What do you mean?"

"Should we head back and regroup with the others? Call the remaining four here? Or continue exploring on our own a bit longer?"

"Shouldn’t we hear the details from Ziel first before deciding?"

Eunice nodded, agreeing that made sense, and Ziel began to explain.

As soon as he arrived, he had discovered the drainage mechanism. Then, a metallic door on the second floor had opened, and from beyond it, four figures had emerged—figures he had just finished confronting. The figures had emitted red and yellow lights and seemed to be saying something—perhaps words.

"Ziel, how did you even recognize it as language? Even modern speech has traces of ancient dialects, but you don’t exactly get exposed to other languages."

"Now that you mention it… maybe it was just because they were humanoid. That assumption might have led me to interpret it as speech."

Ziel admitted it honestly, but Lililia responded, "Ah, no, that’s not what I meant."

"It definitely was an ancient language. But what’s amazing is that you recognized that."

"…Wait, does that mean you understood what they were saying?"

"There wasn’t much to it. They said things like 'Leave' and 'Warning'—pretty much what you imagined. Eunice, did you pick up anything else?"

Klaha was still surprised that Lililia had understood the ancient language, and Eunice, when prompted, simply responded, "No, about the same as you."

"At the very least, we now know this facility was protected by some highly advanced magical devices."

"Magical devices… You mean those figures?"

"I’m not a specialist, so I’d rather confirm with the other four first, but yes. More importantly, I’m curious about what’s beyond the door they came from. I want to check it out."

Eunice turned his head, as if searching for something. Ziel, too, seemed momentarily lost in thought, while Lililia, as if deciding this wasn’t her responsibility, remained motionless. That left Klaha, who was still curious about the figures, to be the first to spot it.

"There. It’s a bit far, but there's a staircase leading to it."

Their footsteps echoed sharply against the metal floor—clank, clank, clank. The thin, lightweight panels made the ground feel unsettlingly flimsy. From behind, Eunice muttered, "Air conditioning…"

"Is this it? The drainage control panel?"

"Yeah. It reacts instantly to the lightest touch, so it’s better not to mess with it."

"By the way, is this the button you pressed, Ziel?"

Lililia pointed at something from a distance, and Klaha agreed—it had to be. The panel clearly displayed an image conveying the message 'Drain the tank.' They didn’t know how hard Ziel had pressed it, but if it was really that sensitive, anyone could have triggered it by accident.

"A thoroughly visualized system. That would mean this place is quite…" Eunice trailed off.

But he didn’t finish the thought. Instead, he quickly averted his gaze.

"Ziel, can you open this door?"

"Eunice, you’re acting like the guy in mystery novels who’s about to die."

"Oh, I am? Whoops."

"When I tried earlier… No, it’s no good. It won’t budge now."

Ziel immediately demonstrated. He grasped the circular handle with both hands, bent his arms, and strained, but the door didn’t move an inch.

"It opened when the figures appeared, so it must be structurally possible to force it open, but…"

"We probably shouldn’t. You’d just break the doorknob. …Wait, so this thing locks with magic?"

"It’s not a magic seal, it’s a magic key."

"What’s the difference?"

"Unlike the figures or the alarm, this door is physically locked, so disabling magic won’t help. If doors weren’t designed this way, mages could just open everything with spells."

"Still, that’s surprising," Eunice remarked.

As Klaha wondered what was surprising, three possible solutions surfaced in his mind.

First, they could destroy the door. Maybe not him, but the others could.

Second, they could call Dewey. If the door was physically locked, someone strong might be able to break through.

Third…

"If those figures could open the door, doesn’t that mean they might be the key?"

With a swift movement, Ziel leapt down from the second-floor passage.

Uwa

Klaha almost let out a sound. To Ziel, it was probably just a casual movement, but since it was not something humans frequently did, it always caught her off guard. Still, she quickly realized that developing a sense for positioning required that kind of ease. Just as she was absorbing that lesson—

A clank sounded.

"Wanna give it a try?"

He's back.

Holding the motionless doll in his arms.

"For example, we could try opening it with this arm."

Saying that, Ziel immediately put it to the test. He gripped the doll's hand from above and attempted to turn the handle.

"Doesn’t seem like it works."

"It’s a magic tool, after all. Even if it has a locking function, it probably needs to be activated by magic. Let's try moving it a bit."

"Alright, I’ll solidify it."

As they spoke, Eunice and Lililia did exactly as they said.

Crimson light once again lit up in the doll’s eyes.

"—!"

"Whoa. That was loud."

"My ears are going to break. Let me mute the sound for a bit."

As if it were nothing, Eunice said that, and soon, the sound nearly disappeared. It wasn’t completely gone, meaning he likely interfered with the air around their heads rather than the doll itself. But even so, his capabilities were overwhelming.

The terrifying part was that, based on their journey so far, Wilae and possibly even Roylen could probably do something similar just as easily.

Klaha reaffirmed her thoughts—she was part of an incredible team.

Because of that, she quickly focused on what she needed to do.

"If this takes a while, should I go call Roylen and the others?"

"I’ll go with you then. I’m not much help standing around here anyway."

"By the way, Eunice, how are we handling the big decision?"

"Ideally, I’d like to check ahead before calling them. Dewey and Ney are over there, so I’d prefer to assess the combat risks and keep things under control. Hold on a second. I’ll try this first, and if it doesn’t work, I’ll leave it to you, Klaha."

Eunice adjusted his magic, and the sound became slightly louder.

From what Ziel had said, the doll was speaking. Sure enough, it was repeating phrases in an unfamiliar language. But rather than the words themselves, the tone of its voice and the red glow in its eyes stirred unease.

Among those sounds—

"—"

Eunice chanted something.

Not a magic incantation, just ordinary words in an unknown language.

With that, the color in its eyes changed.

"Oh?"

"Wait, this actually works?"

The doll began moving slowly. It reached out and touched the door handle. A faint light ran across both the handle and the doll's arm, followed by a distinct clunk.

The handle rotated, and the door opened.

"Alright, now—"

"Wait."

Eunice stopped Ziel, who was about to hold the door open. Instead, Klaha noticed a small stream of water gliding across the floor.

The door shut.

And then, it opened again.

"It worked," Eunice said, sounding as if he hadn’t expected it himself.

Beyond the door was a tiny room. But it wasn’t a dead end—there was another door at the far end.

Just in case, Klaha decided to hold the door open. It didn’t seem like the kind that would shut on its own, but it was better to be safe.

"How did you do that?" Ziel asked.

"I just asked," Eunice replied.

"I told it, ‘We have the right to enter. Please verify.’ And then, it dropped its guard and returned to its position. And now, there's another door."

"I missed my chance. Should we bring another doll?"

"Klaha, I used a barrier to prop the door open, so you don’t need to hold it anymore."

"Thank you."

"No worries. Look here."

With Lililia's assurance, they wouldn’t be trapped. Everyone entered the small room, and Eunice quickly pointed at a spot on the wall.

There was a control panel on the inside.

It displayed an open door and a closed door. A few droplets of water remained near the open door icon.

"It’s a kind of internal lock. I figured there would be something to prevent complete entrapment… Looks like this side was the 'inside' after all."

"So that’s why the water moved and… you pushed the door after it shut using water magic."

"Yes," Eunice said, forming a small circle with his fingers—correct. Perhaps due to the situation, his usual awkwardness was gone. His smile was adorable, Klaha thought.

"Still, it’s strange. If a physical unlocking method is this close by, what’s the point of a magical lock?"

"Well, it’s probably just a design flaw from overlapping mechanisms… Anyway, look. There’s another one over here."

Just as Eunice said, there was a similar control panel by the other door.

Ziel stepped forward slightly, shielding him.

"We can press it, right? Step back just in case. We don’t know what will happen."

"No, you can step back too, Ziel. I’ll press it remotely so we can observe from a safe distance."

"That makes sense," Ziel agreed and stepped back. "Learning, huh?" Lililia murmured as she erected another barrier in the middle of the small room. Beyond it, Eunice’s water magic slowly approached the control panel.

They stepped back a little further outside the room to prepare.

"I doubt we’ll trigger an explosion or anything, but stay alert. Worst case, we retreat through the waterway."

"Understood. If that happens, I’ll direct the escape route."

"Think there’s any risk of gas leaks? I’ll prepare for that too."

"Didn’t smell anything weird before, but let’s stay cautious."

"Got it. Alright, here we go. Three, two—"

At "one," there was a clunk as the lock disengaged.

The water shifted, manipulating the mechanism, and the door opened.

Beyond it lay a pitch-black space.

"No immediate threats. I’ll send out a light," Eunice said.

He released a faint glow from his fingertip.

Holding their breath, they watched where the light traveled. It wasn’t particularly strong, just enough to softly illuminate the immediate surroundings. At first, it seemed like Eunice was testing the depth of the space.

But the light just kept going.

"It’s really…"

"Should we move forward with barriers?"

Ziel murmured, and Lililia suggested.

"Wait a sec," Eunice closed his eyes briefly before nodding. "Alright."

They stepped forward cautiously. Lililia adjusted the barriers as they moved. A cold breeze flowed in from ahead.

"Lighting it up."

With those words, Eunice and Lililia both released more light from their hands.

Not strong, but steady. The soft glow spread out in multiple directions, slowly revealing the shape of the space.

And then—

They saw it.

Standing at the bottom of a massive dome, the four of them looked around in awe.