I loved leveling up.
I just plain loved it.
I always enjoyed grinding levels for characters in games, especially in RPGs.
That said, an eccentric quirk—or rather, a fetish—like that wasn't good for anything.
Was I doomed to join some company I had no interest in, work a job I hated, endure abuse from my superiors, and spend my life as a dead-eyed slave whose labor was exploited for meager wages? In the winter of my third year of middle school, I was in utter despair over what lay ahead.
Then, the world reached a massive turning point.
"We interrupt this program to bring you a special news bulletin."
The evening variety show suddenly cut away, replaced by a grave-faced anchor reading breaking news against a backdrop of newsroom staff running frantically in every direction.
Massive cave-ins had occurred simultaneously across the entire world—not just in Tokyo.
As time went on, it became clear that this was neither an accident nor a prank, and certainly not terrorism.
Bizarre expanses spread within the gaping holes left by the collapsed ground. Ridiculously vast underground caverns. Floors, walls, and ceilings bristling with strangely luminescent minerals—an unreal sight. And moving, squishy mizu-manju creatures appearing inside those caverns.
People who had apparently fallen into these mysterious chasms managed to escape and began posting footage of the interior online.
Among those posts, the ones that generated the most buzz were about "people who gained superpowers."
At first, everyone assumed they were fake, but videos showing people producing fire, water, wind, stones, and lightning from their fingertips—miraculous phenomena straight out of fiction—were uploaded one after another.
What was more, the uploaders were all different people, spanning various ages, genders, and nationalities.
Gradually, the world realized this was neither fiction nor a hoax.
"I'm totally serious!! When I killed that mizu-manju down in the hole, the body vanished and this little marble-looking thing dropped instead!!"
"And here's the weird part. For some reason, that marble looked insanely delicious."
"Seriously, it was like my body craved it as desperately as if someone handed me ice-cold water when I was dying of thirst in the desert. Not that I've ever actually experienced that, though."
"I mean, I get it, okay? Logically, I knew it wasn't food, but I couldn't hold back and ate it—or rather, swallowed it whole."
"And right after that, I could suddenly use superpowers!!"
"LMAO"
"Why would you eat a marble, tho? lol"
"Is this dude okay in the head?"
"Bro, didn't your mom teach you not to eat random crap off the ground? lol"
"What a dangerous guy, dead laughing."
"Still, pretty much everyone else claiming they got superpowers is saying the exact same thing."
"So eating the marble(?) that drops when you kill a mizu-manju in the hole gives you superpowers?"
"Isn't this meme getting way too viral worldwide?"
"It's not a meme, it's just a fact."
"Wait, so if I eat a marble, can I use superpowers too?"
"If it's real, that's awesome!"
"I wanna use superpowers too, man."
"Has the time finally come for my hidden power to undergo Awakening...? Be right back, going to check it out."
Like countless others, I gathered information on social media.
In the end, after piecing together the flood of incoming reports and making sense of it all—
"Hmm..."
Completely unimpressed, I casually went back to leveling up in my game.
The whole "superpower" thing sounded mildly intriguing, but by the time I learned about it, the police and the Self-Defense Forces had already cordoned off the areas, making it impossible to get inside.
And so, on the day those chasms—which would later be called "dungeons"—appeared all across the globe, I simply returned to my mundane routine.
—Or so I thought.
Far removed from my carefree attitude, the world was rapidly plunging into an era of violent upheaval.
Details about the "holes" that had opened worldwide—soon universally dubbed "dungeons" across the internet—gradually came to light.
It was said that defeating a mizu-manju inside a dungeon dropped a marble.
It was said that gazing upon this marble instilled a ravenous hunger beyond one's willpower to resist.
It was said that swallowing the marble granted superhuman physical abilities and powers akin to magic.
It was said that once a person swallowed a marble, they would never crave another.
It was said that the acquired powers grew the more they were used, and that physical capabilities strengthened alongside them.
It was said that someone had awakened an ability to discern the nature of objects and people. According to them, this marble was a seed that sprouted superpowers within a human—a [Skill Seed]—and the sprouted ability was known as a [Seed Skill].
The supernatural gifts brought forth by the dungeons—no, the [Seed Skills]—became a tremendous boon to human society and a major subject of research. It was a mysterious power that seemed completely beyond known science. Manifestations varied wildly from person to person, but some even possessed the power to heal wounds and cure illnesses. If the underlying principles could be unraveled, human technology would take a monumental leap forward. People grew ecstatic over the possibilities [Skill Seeds] offered.
—Yet they brought even greater chaos.
The number of dungeons that appeared worldwide exceeded several hundred.
With so many, people naturally slipped past the police, the Self-Defense Forces, and foreign militaries to sneak inside.
The [Skill Seeds], which the state had moved to regulate due to their inherent danger, ended up leaking from the dungeons onto the surface. Japan was no exception.
Superhumans unaccounted for by the government began emerging among the general populace.
Naturally, plenty of unsavory individuals were among them—or rather, it was precisely those unsavory, antisocial elements who rushed to get their hands on [Skill Seeds] and obtain [Seed Skills] first.
Blessed with superhuman physical prowess and powers, these individuals began running wild across the globe.
To make matters worse, conventional firearms proved largely ineffective against them.
To be precise, it wasn't that bullets didn't work at all, but landing a hit on an agile target moving at superhuman speeds was an extraordinary challenge. On top of that, countless individuals managed to walk away without fatal wounds even when struck.
Furthermore, they were still technically citizens, and the confrontations almost always took place in populated urban areas. Thus, while extrajudicial measures had authorized the use of firearms, deploying excessively destructive heavy weaponry was impossible.
Public order deteriorated at a terrifying pace.
The government mobilized police officers, Self-Defense Forces personnel, and soldiers who had obtained [Seed Skills] in an attempt to suppress the turmoil, choosing to fight superhumans with superhumans. This yielded some success, but society never returned to its former peace.
—All of this unfolded within the first three months of the dungeons' appearance.
Then—roughly three months after the phenomenon began—monsters burst forth from dungeons all around the world, spilling onto the surface.
It wasn't just the mizu-manju that dropped [Skill Seeds]. A vast, diverse horde of monsters surged into the open, leveling cities and slaughtering people—only to crumble into sand and perish after an hour or so of activity.
Because many dungeons had materialized in urban centers and densely populated areas, the destruction caused by this phenomenon (later termed a Stampede) was catastrophic.
Yet humanity soon learned that the devastation from that first Stampede had been utterly trivial.
After all, the monsters that had spilled onto the surface back then were "relatively weak" and died quickly after a "short span" of barely an hour.
—"Relative" to what, exactly?
Relative, of course, to the second and third Stampedes that followed.
Naturally, the government launched investigations into the dungeons' depths.
In doing so, a multitude of shocking truths came to light.
It was said that an abnormal space expanded within the dungeons, so vast that grasping its full scale was nearly impossible.
It was said that a dungeon was composed of multiple layers, and the strength of the monsters grew progressively greater in the lower floors.
It was said that within the lower floors, explorers found not just caves, but clearly artificial ruins, skies lit by a sun, forests, plains, lakes, oceans—and even city-like settlements inhabited by monsters that appeared to be intelligent life-forms.
It was said that while slain dungeon monsters vanished without leaving behind a corpse, they dropped items at a set probability. Those items ranged from meat, pelts, claws, and fangs to the weapons and armor they wielded, spherical crystals of unknown purpose resembling [Skill Seeds], and various tools.
It was said that only the mizu-manju were an exception, guaranteed to drop a [Skill Seed] upon death.
It was said that dungeon monsters simply spawned out of nowhere within the labyrinth. They did not breed.
It was said that once the monster population inside a dungeon exceeded a certain threshold, they would invade the surface.
It was said that for unknown reasons, the number and strength of monsters spawning inside grew greater by the day, while the time they could survive on the surface before collapsing grew steadily longer.
It was said, it was said, it was said——.
The government scrambled desperately to handle the recurring Stampedes.
They sent teams into the dungeons to cull the monsters. They sealed off the entrances with thick concrete and metal. They built fortress-like installations around the entrances and monitored them around the clock—
Yet none of it mattered.
The speed at which the monsters multiplied far outpaced humanity's ability to cull them, and sealing the entrances only made things worse. For some reason, an immensely strengthened horde continued to amass inside until, like a balloon bursting from critical pressure, they obliterated the thick concrete and metal barricades, flooding onto the surface in droves.
—The monsters made no attempt to communicate with humans.
In other words, unlike an ordinary war, there was no negotiating a ceasefire, nor was there any middle ground to reach a truce.
This was an existential war against alien life-forms incapable of mutual understanding. What was more, the enemy knew no fear of death, and their numbers and resources were infinite. They truly just welled up out of nowhere.
Humanity had never prepared for a war against such an adversary.
Defeat was inevitable.
The second Stampede occurred one month after the first.
The third Stampede struck two weeks after the second.
The fourth Stampede hit just one week after the third.
A fifth Stampede was never officially recorded. From the fourth onward, the monsters no longer waited for their numbers to accumulate; they poured onto the surface from the dungeons in an unbroken stream.
By that point, Japan's major metropolitan areas, including Tokyo, where dungeons were densely concentrated, had become uninhabitable.
A massive, government-led evacuation took place, scattering the population across the countryside.
Six months after the dungeons appeared.
Rumors circulated that heavy bombing campaigns had been carried out against major metropolitan hubs, including Tokyo. —Yet the monsters did not diminish.
Eight months after the dungeons appeared.
Rumors spread that nuclear weapons had been detonated inside a certain dungeon. —Yet the dungeon remained intact.
Ten months after the dungeons appeared.
Perhaps as a consequence of the mass migration from major cities to rural areas, dungeons began manifesting in regions where none had existed before, and monsters spilled onto the surface there as well.
Approximately one year after the dungeons appeared.
The evacuation zones and regional cities were devastated. Essential infrastructure—electricity, water, gas, and communications—shut down completely, and directives from the Japanese government ceased. From that point on, all information, directives, cautionary notices, and statements from any entity claiming to be the Japanese government vanished entirely.
With all international lines severed, the exact global situation was unknown—though it was safe to assume nations outside Japan had suffered a similar collapse of infrastructure and state functions.
In other words—governments across the globe had fallen, and civilization had crumbled.
Approximately three years after the dungeons appeared.
Even so, I survived.
Humanity was still clinging to life.
Gathering around individuals who possessed the power to repel the monsters, survivors moved from place to place, scraping together food, water, medical supplies, and daily essentials from the wreckage of ruined cities, barely managing to stay alive.
Several such groups existed across Japan, and people referred to them as "colonies."
A trickle of news from other regions made its way to us through refugees who had narrowly escaped the destruction of other settlements. Some colonies also maintained loose ties with one another, sharing whatever scraps of intelligence they had.
I belonged to one such settlement, assigned to defend the camp from attacking monsters while those blessed with exceptional [Seed Skills] ventured out on scavenging runs.
It wasn't because I was strong. Quite the opposite. Because I was weak, looking after the base was the only duty I was entrusted with.
Over the course of those three years, I had swallowed a [Skill Seed] myself. Finding one wasn't difficult. Even the mizu-manju—monsters now known as slimes—routinely wandered outside the dungeons and died, so if you looked around, [Skill Seeds] were scattered all over the place.
The [Seed Skills] they granted varied wildly, and the vast majority were weak and useless in combat. On top of that, the physical enhancements differed from person to person, making those strong enough to stand against the ever-evolving monsters exceedingly rare.
And—the ability I manifested was, regrettably, painfully weak.
[Seed Skill]—[Fool's Sword]
That was the name of the power granted to me.
Curiously, once a [Seed Skill] awakens, its name and exact nature become instinctively clear to the user.
My ability was simply to "materialize a single steel longsword."
And as I grew proficient through repeated use, "special abilities would manifest within the longsword."
In short, it was a [Seed Skill] that let me materialize an ability-imbued longsword and fight with it.
Hearing just that, it didn't sound terrible. But true to the name [Fool's Sword], the ability was foolish—and greedy.
Normally, a [Seed Skill] grew stronger the more it was used. You could call it a skill's growth. And alongside that growth, the user's physical capabilities would be enhanced as well.
That was the norm.
In my case, however, only [Fool's Sword] grew. Not only did my physical abilities fail to improve, they weren't even enhanced in the first place.
It was as if whatever fueled that growth—what might be called "experience"—had been sucked up entirely by [Fool's Sword].
The blade gained the property to mend itself if broken. It even unlocked the ability to fire flying slashes and enhance its own sharpness.
Yet, if I, the one swinging the sword, remained weak, I stood no chance against any monster above a certain baseline. They would strike before I could swing, and even if I did, they would dodge with effortless ease. The sheer, overwhelming difference in physical capability made real combat impossible.
That was why I couldn't leave the colony.
If I tagged along with the scavenging team, I would only be dead weight and put everyone else in danger.
Even so—I didn't want to remain useless.
I wanted to be someone who could help everyone someday.
So on that day, too, I materialized [Fool's Sword] and trained relentlessly, doing everything I could to master the skill and foster even the slightest bit of growth.
Just then, the scavenging unit led by the head of my settlement—the "Holy Knight Colony"—returned.