[ Yuuto Kiba ]
The barrier sealed with a sound like reality itself clicking into place—a deep, resonant thrum that made my teeth ache. The sky above shifted from crimson to something artificial, oppressive, like someone had draped a sapphire blanket over the world. Intricate demonic patterns crawled across the invisible dome, pulsing with energy that tasted of old magic and bad decisions.
Great.
Not only was the entrance to the cave—and the crystallized poison I actually came here for—completely blocked by several tons of scaled nightmare fuel, but now I was trapped in a magical thunderdome with an Ultimate-class monster that Roygun had specifically, repeatedly, emphatically told me not to fight.
The universe really does enjoy my suffering, doesn't it? I thought, watching the nine massive heads sway above me like a pet, that wants to play a death game with it's master.
Another entertainment episode for some entities, "Let's see what stupid situation Yuuto walks into today!" And then they probably say "Oh look, he's trapped with an unkillable monster! Pass the popcorn!"
Won't you?
The clearing around us had become an arena of nightmares. Scorched earth stretched in every direction, cracked and blackened like the surface of a dying star. The trees at the barrier's edge looked petrified—not scared, but actually turned to stone, their branches frozen mid-sway. The air itself felt thick, saturated with so much magical pressure that breathing required conscious effort.
The Hydra's scales reflected the barrier's blue light in nauseating patterns, obsidian plates that shifted and moved with each breath of its massive body. Each head was easily five meters long, serpentine and elegant in the way that apex predators were elegant—beautiful right up until they killed you.
Those yellow-green eyes tracked my every movement, all eighteen of them focused on me with an intelligence that made my skin crawl. This wasn't some mindless beast. This thing was clearly enjoying the hunt.
One head tilted, mouth opening to reveal rows of teeth that belonged in a lifetime dental care.
Purple light gathered at the back of its throat.
Oh, that's not good—
FWOOSH!
The head snapped forward, and suddenly the air was filled with needles. Not metaphorical needles—actual purple crystallized projectiles, each one the size of my forearm, shooting toward me like a shotgun blast of death.
I moved on instinct, my body flowing like water through the gaps in the attack. The world slowed as focus sharpened my senses. I twisted, ducked, rolled to the side. The needles whistled past me—whip-whip-whip—close enough that I felt the displacement of air against my skin.
They embedded into the ground where I'd been standing with meaty thunk sounds.
And then the earth started dying.
The rock where the needles hit didn't just crack or chip. It dissolved. The stone turned dark, then black, then crumbled into powder within three seconds flat. The poison spread outward in a creeping circle, eating away at solid rock like acid through paper.
One needle, I realized, watching the devastation. One single needle hitting me would be enough to put me in a very bad spot.
More like a fatal spot, my brain helpfully corrected. That's not "oh no, I'm injured" poison. That's "you have seconds to make peace with your life choices" poison.
The massive body shifted, scales scraping against scales with sounds like swords being sharpened. All nine heads rose up, towering above me like the world's most terrifying hydrant.
Purple light began gathering in all nine mouths simultaneously.
"Oh, come on!" I shouted at the universe in general. "That's just overkill!"
The glow intensified, building to a crescendo that made the air crackle with toxic energy.
FWOOOOOOSH!
Nine heads fired as one.
The air became a solid wall of purple death—hundreds of needles forming a killing field that covered every possible escape route. The sound was deafening, like standing next to a jet engine made of hate and murder.
No time to dodge. No room to run.
I threw my hand forward, and the moisture in the air answered my call.
A colossal ice wall erupted from the ground in front of me—CRASH—twenty meters wide, ten meters tall, three meters thick. The temperature dropped so fast that frost formed on my eyelashes. Steam billowed around the edges where super-cooled water met ambient heat.
The needles hit like a purple meteor shower.
CRACK-CRACK-CRACK-CRACK-CRACK!
They embedded into the ice with sounds like bones breaking. For a heartbeat, my wall held, the beautiful clear blue marred by hundreds of purple crystalline spikes jutting from its surface.
Then the poison acted.
The ice turned dark around each needle—black spreading like ink in water. The solid structure began to bubble, to hiss, to melt in ways that ice wasn't supposed to melt. The corruption spread fast, racing through the crystalline matrix, turning my defense into a crumbling mess of corroded slush.
The entire wall collapsed within five seconds, falling apart into dark water that steamed when it hit the ground.
I stared at the puddle that used to be several tons of ice.
Note to self: ice is not an effective shield against Ultimate-class poison. Good to know. Wish I'd learned that in a less life-threatening way.
The Hydra's heads swayed again, almost mocking. Like it was laughing at my attempt.
Alright, I thought, adjusting my grip on my sword. Time to see how tough this thing's skin actually is.
I needed to know if my blade would even penetrate those scales. If I was going to use Mist Breathing techniques to take off a head—even knowing it would regenerate—I at least needed to confirm my sword wouldn't just shatter on impact like a cheap knockoff.
The thing is, I had faith. Trust, even.
Not in Riser's regeneration being superior. Not in this monster actually being unkillable.
But in the System.
The System had given me a quest: Slay the Immortal Monster.
Not "survive the Immortal Monster." Not "escape from the Immortal Monster."
Slay.
The System didn't give impossible quests. Difficult? Sure. Painful? Absolutely. But not impossible.
If the System said I could kill this thing, then somewhere in this arena of nightmares was a solution. I just had to find it.
My trust in the System was higher than my belief in this creature's immortality.
I raised my palm toward the Hydra, fingers spread wide.
Energy gathered—not fire, not lightning, but cold. The fundamental absence of heat, concentrated into a single point.
A beam of ice shot from my hand—FWOOOOSH—pale blue light that turned the air itself into frost. It hit the Hydra's main body center mass.
And for three glorious seconds, I thought it worked.
The ice spread like wildfire in reverse—crawling up the massive body, encasing scales and muscle in crystalline prison. It raced up all nine necks simultaneously, freezing each head in place with mouths still open mid-roar. The entire creature became a statue of ice and shadow, perfectly preserved in a moment of rage.
The clearing fell silent except for the faint crack-crack-crack of expanding ice.
"Yeah, I know it's not going to be so easy" I muttered, already backing away. "So get over it already"
As if on cue, the Hydra's entire body began to glow.
Purple light emanated from beneath the ice—sickly and wrong, like watching gangrene spread through frozen flesh. The glow intensified, pulsing with each beat of whatever served as the monster's heart.
The ice started corroding from the inside out.
Not melting.
Corroding.
The clear blue turned dark, then black, then simply ceased to exist as the poison ate away at molecular bonds that shouldn't have been edible. The ice crumbled into dark powder that dissolved into toxic mist.
CRACK! CRACK! CRACK!
The entire prison shattered at once.
The Hydra burst free with a roar that shook the ground—RRRROOOOOAAARRR!—all nine mouths opened wide, displaying fangs dripping with venom that hissed when it hit stone.
"Calm down, will ya? Freezing definitely won't work, I get it, so keep it down!"
Three heads suddenly lunged at me—WHOOSH-WHOOSH-WHOOSH—serpentine necks extending with horrifying speed. Each one moved independently, attacking from different angles to cut off escape routes.
I threw my arm out at the last possible second.
Ice exploded from my palm in a concentrated blast, catching all three heads mid-lunge. The cold hit them like a physical force—CRASH—flash-freezing scales, muscle, and bone in an instant. The heads became sculptures of blue-white ice, suspended in attacking positions like the world's most threatening art installation.
I immediately jumped back, bat wings erupting from my shoulders to carry me away from the frozen heads.
Because I'd learned something important in the last thirty seconds: freezing worked as a delaying tactic, but it wasn't a solution.
I can't keep doing this, I realized, hovering twenty meters away as my wings flapped steadily. Freezing doesn't kill it. It just pisses it off and buys me seconds at best.
And there was another problem I hadn't considered: I couldn't freeze it from the inside.
Most opponents, you could get creative with water vapor—make them breathe it in, condense it in their lungs, freeze their internal organs. Quick, efficient, brutally effective.
But this thing's mouth was full of poison so potent it dissolved ice on contact. My water vapor wouldn't even make it past its throat, let alone into its body where it could do damage.
I needed something hotter. Something that could actually hurt this thing.
I focused on Sword Birth, but this time I gave it specific instructions. The power responded eagerly, always happy to create weapons I could fully control.
A new blade formed in my grip—longer than my standard swords, curved slightly like a katana, with an edge that gleamed with unnatural sharpness.
But the blade itself wasn't the impressive part.
Blue flames erupted along the steel—FWOOSH—intense, scorching, the color of a clear sky before a storm. The temperature around me spiked instantly. The flames didn't flicker or dance like normal fire. They burned steady and hungry, with heat that made the air shimmer.
[ Flame Enveloper + Cremation flames ]
The kind of fire that could burn hot enough to cremate bone to ash.
The three frozen Hydra heads were already starting to corrode from the inside, purple light eating away at the ice prison.
"Let's see how you like this," I muttered.
I pulled my sword back, flames trailing behind the blade like a comet's tail.
Third Form: Scattering Mist Splash.
I spun in a perfect circle, the flaming blade creating a horizontal wheel of fire and cutting force. The technique was designed to blow away projectiles, to create a defensive barrier of severing wind.
With cremation flames added? It became a ring of annihilation.
WHOOOOOSH!
The circular slash carved through all three frozen heads at once.
The ice shattered—CRASH!
The scales split like overripe fruit.
The flesh beneath burned—SIZZLE!
And all three heads separated from their necks in explosions of blue fire and dark blood.
The severed heads hit the ground with heavy THUD-THUD-THUD sounds, flames still consuming them.
For half a second, I thought I'd actually accomplished something.
Then the stumps started moving.
Flesh bubbled and writhed like living clay. New tissue erupted from the wounds—muscle, bone, scales, all growing at a speed that shouldn't have been possible. The heads regenerated in real-time, new serpentine skulls forming from nothing, complete with eyes that snapped open with yellow-green malevolence.
The entire process took maybe four seconds.
Four seconds from decapitation to fully functional heads, complete with working jaws and poison glands.
I'd seen fast regeneration before—Riser could heal from serious wounds in seconds when he was fresh. But this? This was on another level entirely.
This was Muzan Kibutsuji levels of regeneration. The kind of speed where Gyomei had blown the bastard's head clean off with his chained flail, and Muzan had simply grown a new one before his body hit the ground.
"Another failed attempt" I said, hovering in the air while my wings beat steadily.
The newly regenerated heads turned toward me, joining their six siblings in a display of focused hatred.
All nine mouths opened.
Purple light gathered again.
I couldn't find a way to kill this thing. No matter what I tried—freezing, burning, cutting—it just came back within seconds.
The Hydra's heads regenerated fully, scales gleaming like freshly polished obsidian. All nine heads rose up to their full height, towering above me like executioner's axes.
And then they roared.
RRRROOOOOAAAAAARRRRRRR!
The sound was physical—a wall of fury and hunger that rattled my bones and made my ears ring. The barrier above pulsed in response, magic circles spinning faster as if excited by the violence.
The Hydra looked down at me with eighteen eyes full of absolute malice.
I stared back, mind racing through every option I had left.
Enemy with high-level regeneration is a pain in the ass to deal with, I thought grimly. Doesn't matter how much damage I do if it can just grow it back faster than I can destroy it.
Roygun did tell me this being was immortal. She'd specifically said it wasn't using demonic power to fuel its regeneration—it was just naturally unkillable.
But I refused to believe that.
Because if this thing was truly immortal—truly beyond death—then Rizevim Livan Lucifer would have already found it and used it for his insane plans. That psychopath collected powerful beings like trading cards. No way he'd pass up an actually immortal monster.
Which meant there had to be a way to kill it. I just hadn't found it yet.
One of the Hydra's heads launched another volley of poison needles—FWOOSH!
I responded instantly, raising my hand. Multiple ice shards materialized in the air around me—SHING-SHING-SHING—dozens of frozen projectiles that shot forward to intercept the attack.
CRACK-CRACK-CRACK!
Ice met poison in midair, both attacks neutralizing each other in bursts of dark mist and shattered crystals.
Focus, I told myself, watching the Hydra circle me like a cat playing with ball. There must be a way. If I could only take a look at how this being's regeneration actually works—
Wait.
I could actually do that.
I had access to Muichiro Tokito's Demon Slayer Mark. And that mark didn't just enhance physical abilities—it granted access to the Transparent World. The ability to see through an opponent's body, to observe their internal structure, their muscles, their organs, the very flow of blood through their veins.
If the secret to killing this thing was hidden inside its body, the Transparent World would reveal it.
I let the power flow through me, accepting the mark's emergence.
Heat spread across my face—not painful, but intense. The mark manifested like mist condensing into form, cloud-like patterns spreading across my cheeks and forehead. Dark red against pale skin, resembling mist clouds drifting across a sunset sky.
The world shifted.
My vision clarified, sharpened, expanded beyond normal perception. Colors became more vivid. Movement became predictable. And when I focused on the Hydra...
I could see through it.
The obsidian scales became translucent. The thick muscle and bone beneath turned to ghostly outlines. And deeper still, past layers of flesh and armor, I saw the internal physiology of the monster.
Organs pulsed with life. Veins carried toxic blood through a circulatory system that defied logic. Each head had its own brain, its own nervous system, all connected to—
There.
In the mid-section of the body, slightly offset to the right, surrounded by layers of protective muscle and bone.
A heart.
Not a normal heart. This thing was massive—easily the size of a small car—and it beat with a slow, powerful rhythm that sent shockwaves through the Hydra's entire body. Purple light emanated from it with each pulse, flowing through the veins like liquid poison, spreading to every head, every scale, every inch of the creature.
That's the source, I realized, watching the energy flow. That's what powers the regeneration. The heads are just extensions—disposable weapons. But the heart is the core.
No matter how many times I cut off the heads, I couldn't kill this monster. Not while that heart kept beating, kept pumping that purple energy through its body.
But if I destroyed the heart...
A grin spread across my face.
The Hydra must have seen something in my expression—or maybe it was just coincidence—but all nine heads suddenly became more aggressive, more focused, as if sensing the threat had escalated.
"Found you!" I said, blue flames erupting along my sword once more. The Demon Slayer Mark pulsed on my face, enhancing my perception, my speed, my killing intent.
I looked up at the monster with no fear.
Only certainty.
"Time to end this, you oversized gecko."
My wings folded against my back as I dropped to the ground, landing in a crouch. The flaming sword gleamed in my hand, trailing blue fire that left afterimages in the air.
[ Fifth Form: Sea of Clouds and Haze ]
I exploded forward—BOOM—the ground cracking beneath my feet as I launched myself at the Hydra. The technique flooded my body with speed, turning my movements into something beyond normal perception. I became mist itself—flowing, intangible, impossible to track.
The Hydra's heads responded immediately. One by one they lunged—WHOOSH-WHOOSH-WHOOSH—nine serpentine strikes coming from different angles, trying to intercept me before I reached the body.
The first head came from above, jaws wide enough to swallow me whole.
I flowed past it like water around stone, my flaming sword cutting upward in a rising arc—SLASH!
The head separated from its neck in a spray of blood and blue fire.
THUD!
The second and third heads came from either side, trying to crush me between them.
I twisted midair, my body becoming horizontal as both attacks passed above and below me. My sword traced two perfect lines—SLASH-SLASH!
Both heads fell, flames consuming them before they hit the ground.
THUD-THUD!
The fourth, fifth, and sixth heads came together, learning from their siblings' failures, attacking as a coordinated unit.
I didn't slow down.
My blade became a wheel of blue fire, cutting through necks like they were made of paper. Three more heads fell in less than a second—SLASH-SLASH-SLASH!
THUD-THUD-THUD!
The seventh and eighth heads tried to block my path to the body, creating a wall of scales and teeth.
I went through them.
Not around. Not over.
Through.
My sword cleaved through bone and muscle and scales, blue flames burning away everything they touched. Two more heads separated from the body—SLASH-SLASH!
THUD-THUD!
The ninth head—the last one—came from directly ahead, mouth open, purple light gathering for a point-blank poison blast.
Too slow.
I was already past it, my blade cutting through its neck in a horizontal slash that sent the head spiraling away—SLASH!
THUD!
All nine heads were gone.
All nine heads were already beginning to regenerate, flesh bubbling and writhing as new heads started forming.
But I didn't care.
Because I'd reached the body.
The massive heart pulsed beneath layers of scales and muscle, glowing purple with each beat. The Transparent World showed me exactly where it was, exactly how deep, exactly what angle I needed.
I raised my sword high, blue flames blazing brighter than before. The Demon Slayer Mark burned on my face, pushing my body beyond its limits.
"Just Die!"
I brought the blade down with everything I had.
PIERCE!
The sword penetrated scales that should have been impenetrable. It carved through muscle that should have stopped any weapon. It burned through bone and tissue and finally—SQUELCH—it plunged directly into the massive purple heart.
The effect was immediate.
The Hydra's entire body seized up, every muscle contracting at once. A sound erupted from where the nine heads were regenerating—not a roar, but a scream. A sound of pure agony, of something that had never known death finally experiencing mortality.
SCREEEEEEEEEEEEE!
The purple light that had pulsed through the creature's veins began to flicker, to fade, to die.
My sword burned hotter, blue flames spreading from the blade into the heart itself. I could feel it trying to regenerate around my weapon, could sense the desperate attempt to heal even this fatal wound.
But cremation flames kept on burning, courtesy of Flame Enveloper.
The heart blackened, cracked, crumbled. The purple light died completely.
The Hydra's body collapsed.
CRASH!
Several tons of dead monster hit the ground like a falling building, shaking the forest, hard enough to knock me off my feet. My sword remained embedded in the heart, blue flames still burning.
Purple mist began pouring from the creature's mouth and wounds—toxic vapor that spread across the ground like fog rolling in from the sea.
Oh shit.
I spread my demonic wings—FWOOSH—and launched myself into the air, getting as far from it as possible. The mist spread fast, covering the ground in a layer of poison that made the earth hiss and bubble.
I hovered thirty meters up, watching the mist expand below me, wings beating steadily to keep me airborne.
The Demon Slayer Mark faded from my face, the enhanced perception receding as my body returned to normal. Exhaustion tried to set in, but adrenaline kept it at bay.
I looked down at the massive corpse below, at the purple mist still pouring from it, at the blue flames still burning in its heart.
Just defeated an Ultimate-class immortal monster by myself. A tired grin spreading across my face. No backup. No help. Just me, my sword, and my apparently suicidal decision-making skills.
Roygun would definitely freak out when she finds out I fought this thing after she specifically told me not to.
Worth it, though.
My wings folded back into my back as I descended slowly, making sure the purple mist had dispersed enough to safely land. The ground was scorched and corroded where the mist had touched, but the poison seemed to be dissipating now that its source was dead.
As my feet touched solid earth, a familiar blue screen materialized in my vision.
The System's cheerful notification appeared like a reward popup in a video game.
---
*Quest: Slay the Immortal Monster*
*Objective: Kill the Nine-Headed Hydra*
*Reward: 1 Character Card*
*Status: Completed!*
---
I stared at the notification, then at the massive corpse and then back at the notification.
"I did It!"
. . .
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