After returning home with Yuji and Hiiragi-san in tow, I opened the front door and called out to let my mother know I was back.
"I’m home!"
"Welcome back," her voice drifted from the back of the house. As I thought, she was home.
I stepped up into the entryway while kicking off my shoes, beckoning my friends to follow. "Go on. Don’t be shy, come in, you two."
"Right. Thanks for having us," Yuji said.
"Pardon the intrusion!" Hiiragi-san added.
As they were stepping up into the house, the living room door opened and my mother peeked out. "Oh, Daiki? You brought guests?"
"Yeah. It’s Yuji and Hiiragi-san. We need to go over some things for the upcoming sports festival."
"Oh, I see..." My mother turned her gaze toward them with a warm smile. "Welcome, Hirose-kun, Hiiragi-san. It must be a lot of work with the sports festival right around the corner."
"No, it’s not a problem at all," Yuji replied, raising a hand in a polite wave to dismiss her concern.
Seeing that the conversation was threatening to stretch on indefinitely, I stepped in to break the flow. "Anyway, Mom, we shouldn't keep them standing around in the hall. We'll be upstairs."
"Eh? Oh, you’re right." My mother looked a bit sheepish for a moment, realizing she'd been blocking the way.
Ignoring the slight embarrassment on her face, I looked back at the other two. "Alright, let's head to my room."
"Sure. Excuse us, ma'am," Yuji said with a nod as they followed me past her.
Once we reached my room, I tossed my school bag onto the desk and pulled some floor cushions out of the closet. "Have a seat and make yourselves comfortable. I’ll go grab some tea."
"Thanks," Yuji said.
"Thank you," Hiiragi-san added as they settled onto the cushions.
I headed down to the kitchen. I appreciated the hospitality, but we were about to discuss a secret that couldn't leave this room. If my mother thoughtfully decided to bring tea up later, she might overhear something she shouldn't.
Sure enough, when I walked into the kitchen, she was already arranging tea and snacks on a tray.
"Oh? Daiki, did you come down for this?"
"Yeah. I figured I'd carry the tea up myself."
"I was just about to bring it for you, but..." Her eyes drifted to the prepared tray.
"Thanks, Mom. I'll take it from here."
"Alright then. Be careful with it."
That was a close call. I took the tray and headed back upstairs, thinking that if we had started our discussion immediately, she would have walked right in on the most sensitive part.
When I re-entered my room, Yuji and Hiiragi-san were looking over the testing equipment I’d tucked away in the corner with interest.
"Sorry for the wait."
"Ah, Daiki. We were just having a look," Yuji said.
"Go ahead. It's fine." I set the tray on the table and sat down. "Here, have some tea first."
I handed out the cups and took a sip myself, letting the warm liquid calm my nerves for the conversation ahead. Sensing my shift in mood, the two of them set the tools down and drank their tea in silence, realizing the weight of what I was about to say.
After a long pause, Yuji finally spoke. "...So, Daiki? What’s this important talk you dragged us here for?"
"First, take a look at this." I pulled a sheet of paper from Spatial Storage—the record of my test results—and handed it to them.
"This is...?"
"Timing results?" Hiiragi-san noted, her eyes scanning the data. "There are two columns here... a side-by-side comparison?"
When they both looked up at me for an answer, I gave it to them straight. "That is the result of a comparative measurement of the flow of time inside and outside the dungeon."
"What!?" they both exclaimed in unison. It was the exact reaction I had expected.
"Calm down, you two. I’ll explain everything." I made a calming gesture with my hands, waiting for them to process the shock. They took several deep breaths, slowly regaining their composure.
"Okay. Go ahead, Daiki. Tell us," Yuji said.
"Right."
Even though they were clearly still agitated, they were ready to listen. I laid out the details of my experiment. By the time I finished, both of them let out heavy, synchronized sighs.
"This... this makes things even worse," Hiiragi-san muttered. "Forget making it public—just letting the secret leak would cause a global catastrophe."
"Yeah..." Yuji added.
Just as I had done the previous night, they both slumped back and stared at the ceiling, looking completely overwhelmed. I couldn't blame them; the implications were terrifying. I sipped my tea, silently agreeing with their grim outlook.
"So, yeah. That's the situation," I said.
"I won't even ask what you mean by that, but I finally understand why you were acting so serious," Yuji said, his face looking worn out. Hiiragi-san offered a weary, bitter smile.
Deciding it was time to move forward, I clapped my hands together. "Now, those were the results from yesterday... but that was just the beginning. It's not enough data."
"True," Yuji agreed. "As shocking as this is, if we're actually going to explore inside or move the desk, we need to know more."
"Exactly. So, I’m going to resume the investigation now. Do you two want to help?"
They both nodded without hesitation.
"Alright, let's get to work." I stood up and gathered the rest of my equipment. "First things first, what should we check?"
"Daiki, the clock you left inside wasn't broken by slimes even with the entrance closed, right?" Yuji asked.
"No. It was in the corner, so they probably just ignored it."
"Good. Then let’s try this." Yuji picked up the action camera we usually used for dives. "Let's see what it looks like inside when the entrance is closed. We need to know if the exit disappears. If we get locked in from the outside and can't open it from the inside, we’re dead."
"He's right," Hiiragi-san agreed. "We can't do any internal exploration until we know for sure if we can get back out."
"Agreed."
Yuji then reached for a few more items. "And while we're at it, let's set these up too. We can test them all at once." He was holding a pair of transceivers and a digital music player.
Hiiragi-san immediately caught on. "So, if we put one transceiver inside with the music player and we can still hear the music on the other one, it means we can communicate through a closed entrance?"
"Exactly. And if the signal cuts out, it means closing the entrance severs the physical connection between the spaces entirely."
If the entrance closed and the signal died, it would confirm my worst fears about the dungeon being isolated. I pushed the thought aside, not wanting to dwell on the negative possibilities.
"Ready to try?" I asked.
They both nodded, camera and player in hand. I opened the drawer, dealt with the resident slime using a quick dash of salt, and cleared the area.
"Ready here," I said.
"Here too," Yuji replied. He handed me the action camera (already recording), a transceiver with the transmit button taped down, the music player, and a multi-function clock.
Using Psychokinesis, I carefully placed the items into the corners of the dungeon room while keeping my head clear of the drawer.
"Setup complete. Hiiragi-san, can you hear the music?"
She held the second transceiver to her ear. "Yeah, I hear it."
"Then let's begin."
I glanced at the clock on my desk and slid the drawer shut.
The result was instantaneous. The moment the drawer clicked shut, the music from Hiiragi-san’s transceiver vanished into static. It wasn't that the player was broken; the link between the two spaces had simply been cut.
We waited for one minute. It was a short wait by our standards, but with the time dilation, it was more than enough for the dungeon. I grabbed the handle and looked at my friends.
"Ready? Opening it now."
"Do it," Yuji said.
I pulled the drawer open. Immediately, the sound of music drifted up from the drawer, and Hiiragi-san’s transceiver hummed back to life. The equipment was fine. The signal had only been lost because the "door" was closed.
"Daiki, what’s the range on these transceivers?" Yuji asked.
"The box says about two kilometers with a clear line of sight."
"So a thin wooden drawer wouldn't be enough to block a signal that strong..."
"Which means," Hiiragi-san concluded, "the dungeon really is in a separate dimension. The two spaces are only connected when the entrance is physically open."
She was probably right. I looked at the drawer. This wasn't just a drawer; it was a transfer gate, like something out of a sci-fi novel.
"Probably," I said. "But we'll verify the spatial stuff later. Let's get the gear back and check the footage."
I peeked inside. A new slime had already appeared. I salted it, cleared it out, and used Psychokinesis to retrieve our gear. I set the action camera on the table and plugged it into my laptop.
"Playing it now."
The video started with a close-up of Yuji’s face, then mine, before the camera was moved into the dungeon. The angle was a bit skewed, but it gave a clear view of the ceiling—the entrance—and the center of the room.
"The entrance is closing," Yuji narrated as we watched the "sky" of the dungeon vanish into darkness.
A few seconds later, we all let out a collective breath of relief.
"Okay... it looks like the entrance stays there on the inside even when it's closed from the outside," Yuji noted.
"Yeah. I was terrified the exit would just vanish the moment the drawer shut," I admitted.
"We still need to test if we can actually trigger the opening from the inside," Hiiragi-san added, "but at least it's not an instant death trap."
It was a small victory in a sea of troubling data, but we took it.
And then...
"Look. The slime respawned the second the entrance closed," I pointed out.
Sure enough, the footage showed the monster appearing almost instantly. That, at least, was consistent with my previous observations. Our investigation was far from over.