Instinctively, I reached out and grabbed the top of the opening with my fingers, using it as a pivot point to swing my body around so I could dive in. As I did so, I felt a strange resistance—as if I were pushing through some kind of viscous fluid—but my rotational inertia allowed me to break through.

  “Did you just, uh, drop in instead of climb through?”

  Squad Leader Yoshida was standing there in awe of my over-the-top entrance, when suddenly, the door behind us silently shut itself.

  “Ah?!”

  Then a slight vibration shook the area, and the portal vanished.

  “It’s gone?!”

  Pushing past me, Yoshida ran over to where the door had been and started patting the wall all over to try and locate it.

  “Well, looks like no boat retrieval for us after all,” I murmured.

  “Never mind that, Kei... If the dungeon vanished, do you know what that means?”

  “I figure it means we cleared it, right?”

  “Yes, but can you define ‘cleared it’?”

  “Defeating the boss on the bottom floor, I guess? Wait, boss...?”

  It was already a well-known fact that the boss of a dungeon functioned much like its core. Observations of a dungeon that appeared inside an abandoned church in the United States confirmed that a core-like boss monster at the lowest depths created its bottom floor. Also, direct experience from clearing several dungeons had taught humanity the fact that once such a boss was gone and its conquerors had left the area, the entire dungeon would begin to collapse.

  “Are you saying I was the boss?!”

  Miyoshi nodded solemnly.

  “It’s a good thing for the rest of us you’re the type who tends to stick around until everyone else leaves!”

  If my exiting the dungeon had the same dimension-destroying effect as a boss being defeated, I wonder what would’ve happened if I had left first? Dungeons don’t usually collapse while the people who defeated the boss are still inside...but if the boss just waltzed out on its own, technically nobody defeated it.

  Wait...are bosses even supposed to be able to leave dungeons? I can’t imagine that weird resistance I felt when I went through the entrance was somehow related to me being a boss...

  There were theories out there about what might happen to anyone left behind in a cleared dungeon, but with such a small sample size, there was honestly no way anyone could know for sure. God only knows what fate might have befallen any poor souls still inside the area had I exited first.

  “If that’s actually how it works, does that mean whoever creates their own pocket space like that would need to stay inside it indefinitely for it to continue existing?” I mused.

  “Sure seems that way!” Miyoshi replied.

  Though it’s also possible it only vanished because I bade it that mental farewell...

  I frowned.

  “Hm... Looks like the housing issues in major metropolitan areas won’t be going away anytime soon after all.”

  People would have a tough time living in a place that evaporated into nothing every time they left it. They wouldn’t even be able to put any furniture they bought inside it. Even if someone had a powerful enough imagination to create everything from scratch every time, it wouldn’t have an actual address, so they probably wouldn’t even be able to register as a resident.

  A salaryman with no permanent address working for a listed company on the First Section of the Tokyo Stock Exchange... Sounds kinda cool, actually. Whoa—would that mean they wouldn’t have to pay taxes either?

  “Quite the shame,” Miyoshi responded.

  “If anything, there might be demand for these types of spaces coming from laboratories that conduct dangerous experiments...”

  “I’m not so sure about that, considering we have no idea what happens to whatever’s inside these places when they collapse.”

  It would be an absolute catastrophe if pathogens or other hazardous materials inside one of those spaces ended up getting dumped out over a random part of the planet once it collapsed.

  Even if things ended up shunted away forever into some other dimension, the Earth was a closed system, and permanently funneling away matter of some kind could have unknown consequences down the line. For all we knew, the dimension we used as a dump might start funneling something back in retaliation.

  “Though I admit, I can definitely picture some random unscrupulous industrial waste management company opening up their own pocket dumping space,” Miyoshi added.

  “I mean, there have already been certain countries disposing of radioactive waste in dungeons...”

  You know, that might have been one of the reasons our plutonium erasure request was ever accepted in the first place.

  “At any rate, even though we know it’s possible to create our own personal spaces, we probably shouldn’t release this info to the public until the rules get pinned down a little better.”

  “Kei, you do realize you’re literally the only one who can verify anything about said rules at the moment, right?”

  “Urk.”

  We’ve started seeing active efforts to determine how to best incorporate dungeon technology into modern society. For the sake of humanity at large, I’ll probably have no choice but to help out with those efforts in some small way—but I refuse to sacrifice myself for them completely.

  After all, if ten thousand researchers each ask for just a little help, when you add them all together, that little help immediately turns into a big, fat lot. And even though it is physically impossible for a lone Santa Claus to deliver presents to every child in the world, any children who don’t get presents might end up resenting him anyway.

  That’s when I heard a voice call out.

  “Aaah, maaan...”

  Turning to see where the sudden pathetic groan was coming from, I saw Yoshida kneeling on the ground, utterly crestfallen.

  “How are we gonna prove the footage we took back there is real if the damn door’s gone...?”

  “Doesn’t the TV station that’s airing the show handle that?” Saito asked.

  “Are you kidding? There’s no way in hell they’d stake their reputation on our word!”

  I nearly burst out laughing at the way he said it, but at least he was properly self-aware. Anyone with two eyes and a brain would’ve thought it was all staged.

  “Um, there’s a bigger problem, Yoshida...” Jo nervously cut in. “I think both your phone and my camera are still in the ocean back there somewhere...”

  “What?!”

  After Jo had been freed from the siren’s spell and had come to his senses, he’d realized he no longer had his camera. Despite searching for a good while, he had been unable to locate it in the vast ocean.

  Apparently both men’s memories of the period when they had been charmed by the siren were particularly vague, and they had absolutely no idea where they could have possibly dropped their belongings.

  Panicking, Yoshida searched frantically through his pockets, but of course there was no cell phone to be found. He had Jo try to call the phone, but he was only met with the usual recording stating that the number he was trying to reach was not available.

  “This can’t be happening... Did we lose all of that amazing footage?” Yoshida muttered to himself.

  “Unfortunately...” Jo murmured in response, his shoulders sinking. “You are going to reimburse me for the lost camera, though, right?”

  “With no footage? Is this some kinda joke?”

  “This has nothing to do with the footage! What am I supposed to tell management—that it got swallowed up in an ocean hidden behind some mystery door inside the dungeon? They’ll laugh me out of the office!”

  As the two of them went back and forth squabbling over who would pay for the camera, an exasperated smile came to my face. They should just be grateful they’re still alive.

  I felt a tug at my sleeve, and saw Mitsurugi holding her phone up.

  “Yoshimura, Yoshimura!”

  “Hm?”

  “Take a look at this...”

  She showed me a video of me bringing a massive palm strike down toward a giant shark fin.

  “When did you manage to—”

  “It was a spur-of-the-moment reaction. That was pretty cool, you know.”

  Come to think of it, she had already made it to shore by then, hadn’t she?

  If she shows this footage to the two guys arguing over there, they’ll probably do whatever it takes to get a hold of it...

  Following my gaze, Mitsurugi flashed me a sweet smile.

  “Don’t worry, I’ll take good care of this footage.”

  With that, she headed back over to where Saito was. Thankfully, I got the impression she’d be keeping the video to herself.

  “She actually thought you looked cool, Kei. Ah, the misattribution of arousal... Never underestimate the power of the suspension bridge effect.”

  “You can just shut it.”

  I met her brutally honest jab with a light thwap to the top of her head, and the two of us made our way out of the dungeon.

  ***

  “There you are, Miyoshi! Are you okay?!”

  As soon as we came out through the dungeon gate, we were greeted by Naruse, who seemed rather panicked.

  “Why would I not be? Did something happen?”

  “Well, we picked up a dungeon tremor a few hours ago.”

  “A dungeon tremor?” Miyoshi and I asked in unison, turning to each other out of reflex.

  “It was a rather minuscule one, but it was located—”

  “I don’t suppose it was inside Yoyogi, was it?” I interrupted her to ask.

  “Well, it was extremely nearby, but it was hard to pinpoint exactly... How did you know that, though?”

  As Naruse began to inch nearer to us, we were rescued by the buzzing of her cell phone. Reluctantly, she checked the name of the caller.

  “Sorry, I have to take this,” she murmured, then answered the call. Moments later, she was already blurting out a shocked response. “What? A vanishing tremor?!”

  “Hey, any thoughts on this?” I whispered to Miyoshi.

  “I suppose it really was being treated like a dungeon,” came her reply.

  “Think we should submit an honest report?”

  “How do I put this? I think the onus for that decision should be on the source of the problem—the one who decided to go around abusing D-Factors like that.”

  “‘Abusing’? You’re just trying to casually dump all the work onto me, aren’t you?”

  Just as I was about to go off on Miyoshi about how unreasonable she was being, I heard a frosty voice call out from behind me.

  “Yoshimura?”

  It was summer, but an icy chill ran down my spine nonetheless.

  “Y-Yes?”

  “You know something about this, don’t you?” Naruse smiled congenially as she asked me, but her eyes conveyed an entirely different emotion.

  I froze in place.

  “Uh? Ummm, well, I’m not sure if ‘know’ is the right word...”

  H-Hey, Miyoshi! I reached out telepathically. Earth to Miyoshi...?!

  But she had already made a break for it over to Saito and Mitsurugi, who had just gotten out of the changing rooms, and was inviting them to the YD Café. She gave me a brief little wave, but the tongue sticking out of her mouth did not escape my keen eyes.

  Oh, that sonofa—!

  I couldn’t tell if it was an actual telepathic response or if I was just hearing things, but the words I am no one’s son seemed to ring in my head.

  “Yo-shi-mu-ra?” came Naruse’s chilling voice again.

  “Yeek!”

  And so that memorable summer came to an end, with a harsh session of questioning and scolding from Naruse. I was beginning to realize that we had a long, long road ahead of us before we could release any info on creating personalized environments using D-Factors.

  Annotations

  Message from Ambrose Bierce: Regarding Ambrose Bierce’s last letter, “As to me, I leave here tomorrow for an unknown destination,” which Japanese Wikipedia interprets as “I have no idea where I will be heading.” However, your author chooses to believe that whether Bierce committed suicide or was executed, the sentence in question probably just indicates that he was headed to a destination he had never been before. (It was a once-in-a-lifetime trip, after all.) However you decide to interpret the letter, though, the fact remains that Bierce went missing after writing it. Where did he disappear to? The answer remains one of the greatest mysteries in the history of American literature.

  Fiat panis: The motto of the FAO (Food and Agriculture Organization of the United Nations).

  FAOSTAT: The world’s largest comprehensive online database of information relating to food, agriculture, forestry, and fisheries, managed by the aforementioned FAO.

  Up until recently: Yield numbers as of volume 7.

  The pretend Shadow over Innsmouth thing: A reference to “Ashes to Ashes,” a bonus short story for people who purchased volume 2. It also happens to be included in this very collection. The story is about being manipulated by a Wakasa Bay mermaid into infiltrating Y’ha-nthlei and assaulting a gathering of Deep Ones. (That was my personal impression of it, anyway.)

  “Winter Riviera”: A hit song by Shinichi Mori—his fifty-sixth single. The lyrics give off pretty much zero in the way of Riviera vibes, and anyone singing it could probably swap the chorus for “Winter (insert coastal town here)” without people batting an eye. It’s kind of impressive, really. By the way, the Côte d’Azur is the French portion of what’s known as the Riviera, a coastal area stretching from Italy to France.

  Failed teleportation attempt: This happened in the web version. In the published version, Yoshimura is set to fail this somewhere around volume 11.

  Original version: This may be hard to believe, but Sharktopus was actually a remake of an older movie. In the original film, Shark - Rosso nell’oceano (released overseas under titles such as Monster Shark and Devil Fish), the monster wasn’t a shark at all, but a hybrid of an octopus and a creature from the Paleozoic era. Seriously, of all the movies out there, I can’t believe someone decided to remake that one...

  What happened on the tenth floor: A reference to the undead escapade from volume 5, which is absent in the web version. Well, hopefully any web-only readers can ignore it and just assume something happened on the tenth floor... Though I guess there probably aren’t too many readers like that out there.

  Scandinavian coast: Copenhagen lies in a peculiar location that’s not necessarily on the Baltic Sea or the North Sea. Strictly speaking, the Øresund strait (a redundant term!) isn’t considered part of either sea.

  By the way, if you look at the shore opposite the “Little Mermaid” statue, which earned a coveted spot on Japanese “three most disappointing tourist attractions in the world” lists, you’ll see a billboard for Mikkeller (which is a craft brewery—though I don’t know how they get off calling themselves a brewery when they don’t even have their own brewing facilities). A bit south from there, you’ll find the famous restaurant, Noma. The area used to be a bit run-down, and the street behind the restaurant still tends to be littered with trash sometimes, which makes me kind of wonder why they moved there in the first place. Maybe there just weren’t any other places suitable for urban farming.

  Speaking of Noma, its ostensible sister restaurant, Inua, which had taken up residence inside the Kadokawa Fujimi building, unfortunately ended up shutting its doors in March of 2021. Apparently this was due to both their yearlong closure during the coronavirus outbreak, and Chef Frebel’s decision to return to his home country due to a family emergency. Unavoidable, but unfortunate.

  Siren: The Japanese Wikipedia entry for “Siren” claims that in Greek, the word “πτερνγιον” can mean both feather and scale, which may have been why the lower half of sirens changed from birds to fishes. (Note: As of mid-2025, this claim is no longer present on the entry in question.) This is quoted verbatim all over the internet, but just between you and me, I think it might actually be a typo for “πτερυγιον” instead. I’ll add that your author’s Greek is even more dubious than Yoshimura’s French, so I’ll wait for someone more knowledgeable to chime in.

  Commentary

  Okay, so I got a little carried away.

  As I explained in the foreword, three characters made appearances here that hadn’t yet shown up in the published volumes at the time (though two of them were technically only name-dropped).

  Truth be told, I didn’t even realize my mistake until after I had finished writing... I was already in the throes of postvolume celebration, with absolutely no time left to edit anything out—though the story would’ve fallen totally flat without Ms. Maker, honestly. Besides, I had already made the same mistake with the volume 2 short story, so I figured no big deal; it was probably a forgivable offense for a novel originally released online. And so, banking on the generous hearts of my beloved readers, I ended up releasing the story as is.

  Now, in the coming age when anyone has the ability to create anything using D-Factors, the very concepts of nations and commerce will no doubt be thrown into a state of cataclysmic change. The production industry and the service industry will merge, and everything except for the service industry and certain infrastructure industries will either be wiped out or reduced on a massive scale. At first, people will try to maintain some diversity of products, but while people will recognize the dangers of becoming so reliant on D-Factors, a counterargument will surface that humans already rely on many different things to live, like air, water, and so on and so forth, so what’s wrong with adding one more thing? That will likely cause a gradual decline in production, largely due to cost.

  Paper money and coins will no doubt disappear, but currency as a concept will likely live on as a means of value exchange—at least until people figure out how to manipulate bank account balances using D-Factors.

  I’m ever so curious to see what kind of mental gymnastics nations will have to use in coming up with new taxes to make up for the lack of revenue under the old rules. Perhaps minarchism will reach its peak, birthing the ultimate form of small government.