The red eyes were drawing closer.
Thoom. Thoom.
The ground shook with every step.
There was nowhere to run. The door was shut.
No potions, either. My only weapon was a single rusty knife.
"...You've gotta be kidding me."
I raised the knife with trembling hands.
The black hulk lifted its arm high.
A fist of steel, thicker than a log.
Here it comes—!
GRAAAAAAAAH!!
The roar slammed into my eardrums.
The fist came crashing down.
I threw myself sideways, practically rolling.
KA-BOOOOOM!!
The floor where I'd been standing shattered to pieces.
If that had hit me, I'd have died on the spot.
My heart felt like it was about to explode.
But—strangely enough, my head was cool.
(After it brings down its right fist, its left shoulder is wide open for half a second.)
At the last possible moment, my body had been watching on its own.
It was the one thing I'd always been good at.
A tiny eye for observation that no one ever praised me for.
The hulk raised its arm again.
I kept tracking its movements with my eyes.
The twist of its muscles. The shift of its center of gravity. The seams between its steel plates.
Ever since I'd started diving into dungeons, I'd figured out one thing.
I can't fight. I'm not strong.
But when it comes to "seeing," I'm faster than anyone.
With the very eyes Takumi and his crew had laughed off as "just a lucky guess from good instincts."
Right then, on the steel plate of its left shoulder—a single crack.
A faint fissure, like an old scar.
There.
For some reason, I was certain.
That was this thing's "weak point."
I pulled Dad's stone out from the bottom of my backpack.
Blackiron Steel. Worthless junk.
The moment I gripped it, the stone flared hot.
"...Ngh!"
I pressed the stone against the rusty knife.
And then—the blade began to glow black.
I had no idea what was happening.
But there was no time to think about it.
Blackiron Steel—a rare ore that cleaves only monsters of steel, made for taking down secret bosses.
I only learned that after it was all over.
"This one thing—keep it on you, always."
I thought I heard Dad's voice echo somewhere deep in my head.
Could it be that Dad...
knew what this stone really was—?
The hulk's fist came swinging down.
Now.
I kicked off the ground.
I slid right under the descending arm.
The crack in its left shoulder.
Straight at it, I threw a punch with my whole body weight behind it—
"Raaaaaaaaagh!!"
I drove it home.
THOOOM!!!
A dull sound. The impact felt as light as a feather.
An instant later,
cracks raced across the hulk's entire body.
Crack, crack, crack—
Light leaked out from inside.
And then—
BOOOOOOOOOM!!!
The jet-black secret boss shattered into pieces.
"...Huh?"
As I stood there frozen, particles of light swirled up in front of me.
I'd beaten it.
A monster like that, with one hit.
My knees were shaking like crazy.
I'd made it. I was going home alive. That alone was almost enough to make me cry.
At my feet, a treasure chest unlike any I'd ever seen had appeared.
The secret boss's drop. It had to be something insane.
But right now, I had bigger things on my mind.
That was when—
In my pocket, my phone was vibrating like it had gone haywire.
Bzzzzzzzzzzt!!
I pulled it out and looked at the screen.
"LIVE NOW"
The viewer count was spinning upward at a ridiculous rate.
12,847... 89,201... 503,668...
"...What."
The comments were pouring down like a waterfall.
"DID YOU SEE THAT!?"
"ONE PUNCH!!??"
"one-shotted the hidden boss 'Hellsteel King' LMAOOOO"
"who IS this streamer!? ZERO subs!?"
"making a clip"
"SPREAD THIS!!!!"
"wait, this isn't a bug for real, right?"
"bro that's a hidden boss even the admins haven't found"
"a god-tier channel has descended"
"a genius has appeared"
"how tf does this guy have zero subs, this makes no sense"
The numbers wouldn't stop.
One million. Two million. Three million.
It had to be that bug.
The "Streaming function: Rebooting" on my phone back then.
The stream I thought I'd turned off had switched itself back on.
Right in front of the whole world, of all things.
"W-wait, hold on, this is...!"
Even my trembling voice
was being streamed live to the entire world.