The Demon Slayer Corps.
An organization that had endured for centuries its sole purpose the destruction of Muzan Kibutsuji.
At its core stood the Ubuyashiki Family, generation after generation offering unwavering support, guiding the Corps from the shadows.
That evening, Kagaya Ubuyashiki returned home.
Inside, his wife, Amane Ubuyashiki, was gently lulling one of their daughters to sleep.
"I'm home," Kagaya said softly, careful not to disturb the quiet atmosphere.
Amane glanced up, immediately noticing the faint smile resting on his lips.
"…Something good has happened."
Kagaya nodded.
"Today, Rengoku Shinjuro informed me that his wife has found a physician capable of treating her illness."
Amane's expression softened.
"That is indeed wonderful news."
Before their conversation could continue, the child in her arms suddenly began to cry.
"Wah… Wah…"
Kagaya froze, visibly at a loss.
Despite his position, despite his wisdom he was still young, barely past childhood himself.
Amane couldn't help but smile faintly at his flustered reaction, gently rocking their daughter while humming a soft lullaby.
Gradually, the crying subsided.
The child drifted back to sleep.
Kagaya exhaled quietly.
"…I am utterly incapable in matters like this."
Amane reached out, drawing him closer.
"Outside, you support the entire Demon Slayer Corps," she said gently. "Here… allow me to support you."
Their marriage had not begun with love.
Yet, over time, something deeper had taken root.
At dawn, Kagaya stood before the graves of fallen Demon Slayers.
This was his daily ritual.
If he could not fight on the battlefield, then he would honor those who did.
Yet
It was not enough.
His thoughts turned, as they often did, to Muzan.
Elusive.
Untouchable.
Even after centuries, the Demon Slayer Corps had yet to locate him.
And their strength…
Was it sufficient?
At present, their most capable swordsman remained Shinjuro, the Flame Hashira. Alongside him stood Gyomei Himejima, newly risen yet already formidable.
But the remaining Hashira positions lay vacant.
A dangerous imbalance.
Kagaya lowered his gaze.
"…Can this curse… truly end in my generation?"
Within the depths of the Infinity Castle, Kokushibo knelt before Muzan, reporting the outcome of his mission.
Muzan listened in silence.
The revelation that the target had already been eliminated was unexpected.
Yet he did not question Kokushibo's account.
"…Very well," Muzan said at last. "You have done well."
His current form a refined woman stood in stark contrast to the oppressive aura he exuded.
Kokushibo remained silent.
Outwardly composed.
Inwardly…
There was a faint sense of discomfort.
No matter the form Muzan adopted, the presence beneath it remained the same.
Unchanging.
Unsettling.
Muzan stepped closer, placing a hand lightly upon Kokushibo's shoulder.
"There is no need for concern. Continue as you have."
With that, he turned and departed.
For a moment, Kokushibo watched him go.
"…He changes faces as easily as others change garments."
Nearby, Nakime continued to play her biwa, her expression as unreadable as ever.
After a pause, she spoke.
"…It is merely preference."
Kokushibo said nothing further.
Returning to his residence, Kokushibo entered a quiet chamber.
It contained a training ground… and something else.
An empty space.
Too open to be practical.
Almost… nostalgic.
After a moment, he began searching.
Drawers.
Cabinets.
Hidden compartments.
At last
He found them.
Two kites.
Their surfaces bore names.
One read: Yoriichi.
The other: Kokushibo.
For a brief moment, time seemed to still.
These were remnants of a distant past of a life long since abandoned.
Just like the flute he had once kept.
Silently, Kokushibo stepped outside.
The kites rose into the night sky, carried by a gentle wind.
He watched them in silence.
Memories faint, fragmented lingered at the edge of his mind.
And for that fleeting moment…
Even time itself felt insignificant.
Two years passed.
The flow of events shifted subtly, shaped by Kokushibo's interference.
One change, however, stood above the rest.
The resignation of the Flame Hashira.
Ruka Rengoku's illness could not be cured overnight.
Under Tamayo's treatment, it took years of careful care before her condition finally stabilized.
But that very process gave rise to suspicion.
Tamayo appeared only at night.
Never during the day.
Eventually
Shinjuro realized the truth.
She was a demon.
One evening, he confronted Kokushibo.
"The physician you introduced… is a demon."
His voice was steady, though tension lay beneath it.
"…Did you know?"
Kokushibo did not deny it.
"You discovered it," he said calmly. "And yet… you did not strike her down."
Shinjuro's grip tightened.
His thoughts were in turmoil.
"Tell me," Kokushibo continued, "does she deserve death?"
The question struck deeper than any blade.
By all logic
Demons who consumed humans deserved to die.
That was the unshakable truth of the Corps.
And yet…
Tamayo had saved his wife.
Protected his family.
For the first time in centuries, that absolute truth had been challenged.
"…Did you report this?" Kokushibo asked.
Shinjuro shook his head.
"No. I alone know."
Kokushibo's senses extended outward.
"…Where is your family?"
"They have gone out."
Silence fell.
Shinjuro's conflict deepened.
Duty.
Gratitude.
Both demanded opposing actions.
Kokushibo exhaled slowly.
Enough.
The time for concealment had passed.
"…Then allow me to answer your question."
His form shifted.
Six eyes opened.
His true nature revealed itself without restraint.
"I am a demon."
For a brief moment, Shinjuro froze.
Then
Steel rang out.
His Nichirin Blade flashed into his grasp.
Instinct overrode hesitation.
Their swords collided instantly, sparks scattering into the night.
Kokushibo stepped back, moving toward the open courtyard.
Fighting inside would be… inconvenient.
Shinjuro followed without pause.
Flames surged around him as his breathing sharpened.
Kokushibo's presence darkened.
"I regret this," he said quietly. "You are a man worthy of respect."
His killing intent surged forth vast, suffocating.
The night itself seemed to tremble.