Yōsuke delved deeper into the demon's memories, probing further into the tangled remnants within Maedō's (the captured demon's) mind.
Within that chaos, he noticed a faint glimmer of light. When he touched it, a fragment of the demon's memories as a human unfolded before him.
Before becoming a demon, the boy called Mandō had been an abandoned orphan, wandering from town to town with other homeless children.
It was an age of famine — ordinary people could barely survive, let alone feed the children of the streets.
One day, driven mad by hunger, the boy used a shard of a broken mirror to kill another child… and ate the corpse.
From that day onward, his descent could not be stopped.
One by one, the children he once huddled beside were slaughtered and consumed by his own hands.
When no other vagrant children remained, he used his cherubic appearance to deceive kind strangers who offered him shelter — only to murder them, too.
The memory ended abruptly.
Yōsuke furrowed his brow.
Throughout all of it, he hadn't sensed even a trace of human emotion — no anger, no pity, no remorse.
Only the primal instincts of a beast.
Venturing deeper, Yōsuke uncovered another fragmented vision — Mandō and Kokushibō carrying out a mission together.
Only one phrase echoed within that memory:
"The Ubuyashiki cursed bloodline."
Yōsuke withdrew from the memory, his expression grave.
"The Ubuyashiki… curse… bloodline… What exactly are they searching for?"
If their goal had been the Blue Spider Lily, that would make sense.
But this… this was something else entirely.
"Master, did you find anything useful?" asked Shinobu, seeing his pensive expression.
"A little," Yōsuke replied. "But it's fragmented. Continue your research — I need to step out for a while."
A thought stirred within him: the records Ryūgaku (Kaigaku) had stolen from the Corps headquarters — the ancient documents detailing the Ubuyashiki family's thousand-year history.
Something in his gut told him the two events were connected.
Yōsuke soon arrived at the Ubuyashiki estate.
He went directly to Kagaya Ubuyashiki and spoke without preamble:
"Kagaya — those documents Kaigaku stole, the ones about the Ubuyashiki lineage… what exactly was written in them?"
Seeing Yōsuke's uncharacteristic gravity, Kagaya answered plainly, "They contain records of our family's history — of the curse placed upon us generations ago."
At that, Yōsuke's eyes widened in realization.
The pieces suddenly fell into place.
"I think… I understand what Kibutsuji Muzan has been searching for."
Kagaya was puzzled. "Besides the Blue Spider Lily, what else could he possibly want?"
Yōsuke's face grew ashen.
"It's troublesome, Kagaya. Muzan is searching for the descendants of the Priest Clan — the ones whose blood once allowed your cursed lineage to survive."
"The Priest Clan?" Kagaya repeated. "What would Muzan want with them?"
Yōsuke explained:
"After Muzan and I became demons, the Ubuyashiki family's bloodline was cursed. Every child born into your family would die young.
But when an Ubuyashiki man wed a girl from the Priest Clan, the curse would weaken — the bloodline would stabilize. That means the Priest Clan's blood contains a unique power."
Kagaya frowned. "But it only suppresses the curse, not cures it. Muzan shouldn't gain anything from that, should he?"
Yōsuke's tone darkened.
"What if… the Ubuyashiki curse is a form of partial demonization — and the Priest Clan's blood suppresses that process?
What if their blood can even allow demons to withstand sunlight?"
The realization struck Kagaya like a blow.
"You're saying Muzan plans to use the Priest Clan's blood to overcome his greatest weakness — the sun?
Compared to chasing the elusive Blue Spider Lily, that would indeed be far more achievable…"
"Exactly. It's just a theory," Yōsuke said grimly, "but we must prepare for the worst. Kagaya, do you know where the Priest Clan is now?"
"I don't," Kagaya admitted. "The Priest Clan hides deep within the mountains. But perhaps my wife, Amane, may know something."
Amane Ubuyashiki — once a daughter of the Priest Clan — was summoned and told everything.
After a moment of reflection, she answered,
"I no longer know where the Priest Clan resides. Each time one of our daughters is wed into the Ubuyashiki family, the clan moves to a new location. When I was married into this family, they had already moved away, leaving no trace behind."
Yōsuke pressed further. "Amane — what can you tell me about the High Priest of your clan?"
Amane hesitated, then said quietly:
"The High Priest is the messenger of the god we serve — the one who delivers all divine revelations to our people.
For a thousand years, every divine oracle has come through the High Priest."
Yōsuke's eyes widened. "A thousand years? You mean the same High Priest has lived that long?"
Amane shook her head.
"I don't know. I have never seen the High Priest myself — nor heard of any ritual to appoint a new one."
A chill ran down Yōsuke's spine.
If, for nearly a thousand years, another being besides himself and Muzan had survived the flow of time — untouched by age — and yet remained hidden from his sight…
How terrifying must such a being be?
Even the physician who had once turned him and Muzan into demons now came under suspicion in his mind.
That single potion — to create two immortal demons — had always seemed far too convenient.
And the children born of the Ubuyashiki and Priest Clans — they could suppress the curse, and foresee the future, even evade Muzan's gaze.
Could that "foresight" itself be a form of Blood Demon Art?
It felt as if an unseen hand — vast and cold — was quietly pulling the strings of fate.
Yōsuke returned to the Butterfly Estate, his thoughts clouded.
Images of the Priest Clan and the mysterious High Priest consumed his mind.
So many questions circled endlessly:
Was Muzan truly searching for the Priest Clan?
Did the ancient physician deliberately create him and Muzan for some hidden purpose?
Could the Priest Clan's blood really allow a demon to endure sunlight?
Does the High Priest still live — and if so, is he human, demon, or something else entirely?
And if all of this was orchestrated from the start… what end was it meant to achieve?
Overwhelmed, Yōsuke summoned the System for the first time in a long while.
"System… is this world truly the same Kimetsu no Yaiba world I remember?"
[Ding! If it matches the world within your memories, then yes — it is.]
"I may have forgotten many details, but I still remember the broad shape of this world…
Yet now everything feels unfamiliar — as though I've stepped into a distorted version of it."
[The future is not fixed. The moment you appeared in this world, its future began to change.]
Yōsuke fell silent.
"So… all of this — the chaos, the divergence — is because of me?"
He rubbed his temples wearily.
The tangled ties between the Ubuyashiki family and the Priest Clan grew more complicated by the moment…
and the mysteries around them — deeper still.