It had been a month since their last meeting.
The morning air at Demon Slayer Corps Headquarters felt heavier than usual, quieter somehow—as if the very earth was holding its breath.
From within the eastern compound, the head of the Ubuyashiki family, Kagaya Ubuyashiki, walked silently toward the residence of Tachibana Kyūjō, accompanied by Lady Tamayo.
Kyūjō, seated beneath the wooden awning, turned his gaze toward them. A moment of surprise flickered in his eyes, but it quickly faded. A soft, almost wry smile touched his lips.
He looked to Tamayo and asked calmly,
"So… it's ready, isn't it? The medicine that stops the body from exploding."
Tamayo nodded gently and reached into her sleeve, producing two small glass vials. One held a thick crimson liquid. The other, pitch black.
"The red one… is for Muzan Kibutsuji," she explained. "The black one is prepared for Kokushibō. We're still unsure if he possesses the same extreme regenerative ability as Muzan, but… it's better to be ready."
These weren't ordinary serums. Tamayo had analyzed the remains of elite demons and fused what she'd learned with the last remnants of the Demon King's blood.
The result—two formulas, each tailored to match the biology of their respective targets.
Kyūjō accepted the vials with both hands, careful not to even jostle them.
"How do I use them?" he asked. "Injection?"
Tamayo nodded again, this time more firmly.
"If you're sure you'll use it within thirty minutes, you can draw it into a syringe ahead of time. Otherwise…" she paused, "just touching an open wound will be enough to activate the compound."
There was a beat of silence.
Then, in a quieter voice, Tamayo asked:
"…Kyūjō-san. Are you sure about this? Can you really face… both Demon Kings at once?"
Kyūjō lowered his gaze, fingers brushing his chin as if in deep thought.
He was recalling every detail he could from the original battle inside the Infinity Castle—every clash, every failure, every shred of chaos that had once consumed that final arc.
Then, with a breath that sounded far too steady for someone preparing to walk into death's jaws, he met their eyes.
His voice was calm, resolute.
"If Muzan truly takes the bait—if the Blue Spider Lily draws him out…" ʀᴇᴀᴅ ʟᴀᴛᴇsᴛ ᴄʜᴀᴘᴛᴇʀs ᴀᴛ novｅlfire.net
"Then he dies by my hand."
"Kokushibō too. It'll end the same way."
"But for the strategy itself… I'll leave it in your hands, Oyakata-sama."
Kyūjō had already spoken to Kagaya about the Blue Spider Lily during a prior meeting, though he'd left the origin of his knowledge vague.
And Kagaya—who understood Kyūjō more deeply than anyone—hadn't asked for an explanation.
He simply… trusted him.
Just as Kyūjō predicted, days after their return to headquarters, the mysterious plant he'd brought back from his journey finally bloomed.
On a clear afternoon, over a dozen brilliant blue flowers had opened quietly among the leaves.
Tamayo had managed to preserve them using a special alchemical solution—keeping the petals, stems, and structure perfectly intact.
Whether the flower's medicinal potency remained… didn't matter.
Because Kyūjō had no intention of letting either Demon King live long enough to try it.
Not even for a moment.
Kagaya nodded wordlessly.
This was the flower Muzan had hunted for over a thousand years—the one thing he believed would unlock the final step of his evolution.
Immunity to sunlight.
For the demons, the Demon Slayer Corps was no longer the threat.
No, the true danger now… was Kyūjō.
And that made the flower the perfect bait.
Even if the trap was obvious, they couldn't afford to ignore it.
Only one flower. Two Demon Kings.
Would Kokushibō kneel and hand the opportunity to his heartless younger brother?
Kagaya exhaled softly.
At long last… the curse that plagued his bloodline would end.
And it would end with this man—the one who had walked through death and returned.
The one who now stood as the Corps' brightest hope.
A rare smile touched Kagaya's lips, genuine and full of quiet pride.
Kyūjō is no longer just a swordsman.
He's the redemption of our entire bloodline.
In a remote valley, far outside the borders of Kumagaya Prefecture.
Kyūjō stood alongside Kagaya and the entire Hashira corps.
The terrain was rugged—tall cliffs, narrow ridges, and boulder-strewn slopes. A place where sound barely traveled and light vanished early in the afternoon.
This hidden valley… had been personally chosen by Kagaya.
Here, the final battle would begin.
The Hashira spent hours inspecting every rock, every crevice, every natural choke point.
They planned, discussed, debated.
Traps were laid beneath the soil. Boulder-falls rigged above cliff edges. Funnel points prepared to isolate and slow the enemy.
For ten days, they transformed this valley into a battlefield built for one purpose:
To kill the Demon Kings.
And today… that plan was set in motion.
Far beyond the reach of villages or cities, deep in the cold mountains...
A demon stirred from slumber.
He had existed for over a century.
His name was Yamabiko, the Child of the Mountain.
One of Muzan's ancient creations—older than many of the Upper Moons.
But unlike the others, Yamabiko preferred solitude.
He didn't crave power. He didn't seek carnage.
He just… wanted to be left alone.
He lived far from human eyes, deep inside a shadowed forest, hidden within an old stone cave.
He only hunted occasionally—small groups of hunters or lost farmers that wandered too close.
During his first decade, humans still tried to fight him.
Once, over a hundred men from nearby villages had climbed the mountain together. They brought bows, spears, even farming tools and kitchen knives.
They never stood a chance.
Yamabiko moved like mist. Struck like stone. He could crush boulders with a single swing. Wounds vanished the moment they were made.
And yet… he didn't kill them all.
No—just practicality.
"Why waste food?" he once muttered to himself.
"If I eat them all now, they'll rot before I'm hungry again. Better to let them go… and come back later. With more."
From then on, the villagers stopped fighting back.
They even started sending children—small, fresh, trembling—to the mouth of his cave.
An unspoken agreement, forged in silence and fear.
Eighty years had passed since that dark contract began.
But Yamabiko's cautious nature—etched into his instincts after a century of survival—wouldn't save him now.
Because the world was changing.
The Twelve Kizuki had crumbled.
One by one, the Lower Moons had fallen.
Muzan had not yet replaced them... until now.
To rebuild his forces, Muzan didn't draw from the rabble.
He searched through the bloodlines he had once seeded, seeking only the strongest survivors.
Six demons were chosen.
Four endured the infusion of his new blood.
And among them… Yamabiko rose again.
Now, he bore a new title:
Lower Moon Three – Yamabiko.
Today was feeding day.
Yamabiko stirred from the back of his cave, his massive body shifting like a landslide.
Slowly, almost lazily, he stepped into the mountain light.
Standing there, at the base of the slope, was a middle-aged man with a faint scar on his forehead.
"Huh? That's odd… Why isn't it a child this time?"
"This guy looks dry and chewy. Who changed the menu without telling me?"
Then the demon chuckled to himself.
"Well… I guess a change of flavor every eighty years isn't too bad."
What Yamabiko didn't realize—what he couldn't realize—
Was that this step forward...
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