Kuroba continued to explain, "The Kasugai Crows cultivated by the Ubuyashiki Family are not ordinary birds..."
"We are an ancient and rare transcendent variant, which can be called 'Spirit Crows' or 'Counseling Birds'."
Cheng Mo listened quietly, the night wind in the mountains rustling his clothes, but he himself seemed to have turned into a block of ice.
"We are born with brain capacity far exceeding that of ordinary birds, which is the foundation of high intelligence."
Kuroba continued.
"From the fledgling stage, we undergo extremely rigorous natural and artificial dual screening. Only the strongest, smartest, most spiritual, and most adaptable individuals to various energy environments can survive."
Cheng Mo could imagine that scene.
Countless young birds struggling in cruel competition, with only a very few able to stand out.
This method of cultivation was ruthless and efficient.
"Individuals who pass the screening," Kuroba's voice held an indescribable emotion, "will undergo an ancient 'Spirit Awakening' ritual presided over by a specialized priest."
Cheng Mo noticed a very subtle ripple in the mind link when Kuroba mentioned "priest."
It seemed to be related to the "priest clan" mentioned earlier.
"During the ritual, an extremely weak, pure 'human soul fragment' is injected into the Spirit Crow's mind," Kuroba explained in a more modern way, "This fragment is not a complete soul, does not carry personal memories and emotions, and is more like a 'blank wisdom template'."
A hint of understanding flashed in Cheng Mo's eyes.
So that was it; this explained why Kasugai Crows could possess intelligence and learning abilities almost human-like.
This was not simple domestication, but a transformation involving the soul level.
"After the Spirit Awakening, there is a long process of learning."
Kuroba continued.
"Through a secret technique similar to 'Mind-Soul Transmission', the Ubuyashiki Clan continuously instills a massive amount of information into the Kasugai Crows."
He listed that information.
"Maps of the entire country, mountains, rivers, towns, villages, and even some secret paths."
"The Demon Slayer Corps' ranking system, intricate rules, various identification codes and gestures."
"The general weaknesses of demons, the approximate characteristics of different Blood Demon Arts, and known information about the Twelve Kizuki."
"Standard language, and even some local dialects, to ensure we can communicate with Demon Slayers or civilians in any region."
National geography, Demon Slayer Corps structure, demon intelligence, various languages... Cheng Mo realized that every Kasugai Crow was a mobile database and communicator, a crucial link for the effective operation of the Demon Slayer Corps.
They learned to speak, a true understanding and expression.
This explained why Kasugai Crows could understand complex concepts such as "slaying demons," "rescue," and "Twelve Kizuki," and make independent judgments.
"When a Kasugai Crow is assigned to a Demon Slayer, a simplified 'Contract Ritual' is held."
Kuroba's voice became somewhat subtle.
"The ritual establishes a shallow, one-way soul link between the Demon Slayer and the Kasugai Crow."
"The main function of the link is that the Demon Slayer can vaguely sense the Kasugai Crow's direction and general state. The Kasugai Crow will naturally develop a sense of closeness and trust towards its host through the link, and vice versa."
Kuroba added, "Moreover, as the Kasugai Crow fights alongside its host for a long time, it will be influenced by the host's personality, Breathing Technique energy, and even emotions, thereby developing a unique personality."
Cheng Mo thought of the Kasugai Crows with their varied personalities.
Some were noisy, some were steady; so that's how they formed.
At this point, Kuroba's tone became solemn: "And the most important point is that the Kasugai Crow is a relay station for the Ubuyashiki Family's 'Heart Reflection' secret technique."
"Heart Reflection secret technique?"
Cheng Mo's pupils contracted slightly.
This term instinctively put him on guard.
He motioned for Kuroba to continue.
Kuroba noticed Cheng Mo's wariness, and a complex emotion flashed in his crow eyes.
"Master, have you already noticed that communicating with members of the Ubuyashiki Clan creates a strange sense of security or trust?"
Cheng Mo remained silent, but his gaze grew colder.
In an instant, scenes of his several meetings with Kagaya Ubuyashiki rapidly replayed in his mind.
That gentle warmth like a spring breeze, that wisdom that saw into people's hearts... that frankness and tolerance he maintained even when facing someone of unknown origin and strange power like him... After every conversation, he did indeed feel that his cooperation with the Demon Slayer Corps was smoother.
His perception of the Master also increasingly leaned towards positive, even... trust.
He had originally thought it was due to the other party's personal charisma and superb rhetoric.
Coupled with his own need for the Demon Slayer Corps' resources, he hadn't delved deeper.
But now it seemed... "This is not an illusion..." Kuroba sighed softly.
"This is the effect of the 'Heart Reflection' secret technique, but it is not a forced mental enslavement or manipulation, but a passive, unconsciously emitted influence at the soul level."
He explained in detail: "The souls of the Ubuyashiki Family members, forged by generations of inherited curses and missions, are exceptionally pure and resilient, like a clear mirror, capable of reflecting the kindness and bright side deep within the other person's heart, causing them to feel a pleasure of being deeply understood and recognized when communicating with Ubuyashiki Family members."
"This is the primary form of 'Heart Reflection'," Kuroba emphasized.
"Anyone who approaches an Ubuyashiki Family member... especially the Master, will be subtly influenced by this aura, and the longer the time, the deeper the influence."
"And the Kasugai Crow, as the being most closely connected to the Ubuyashiki soul, is both a beneficiary and a weak diffuser of this aura."
"So I speculate that the soul fragments implanted in us Kasugai Crows during the Spirit Awakening likely originated from the sacrificed ancestors of the Ubuyashiki Family throughout history."
Cheng Mo stood still, the moonlight illuminating his expressionless face.
He finally understood why the Demon Slayer Corps was so loyal to the Master, even willing to die for him.
This was not entirely personal charisma; there was also the influence of this soul-level secret technique.
"Interesting."
After a long pause, Cheng Mo slowly spoke.
"The foundation of a thousand-year-old family truly cannot be underestimated."
He did not feel anger or betrayal.
Instead, he was analyzing all of this with an almost cold rationality.
This was a strategy for survival... To combat Muzan and the curse, the Ubuyashiki Clan had indeed developed every usable power to its extreme.
From body to soul, from human to bird... This extreme obsession with achieving a goal by any means necessary, in some respects, bore a striking resemblance to him.
It was just that the other party used the subtle "reflection" and "resonance" of a needle hidden in cotton.
While he preferred the straightforward "transaction" and "control."
He looked at Kuroba on his shoulder: "Can you be immune to this secret technique?"
"I can now, Master," Kuroba replied respectfully.
"Your absolute contract has covered and isolated all external soul influences."
Cheng Mo nodded, his gaze once again directed towards the waterfall cave.
The Ubuyashiki Family's soul secret technique, Xue and Ying's soul symbiosis, Muzan's corruption of souls... The mysteries of the soul in this world were far deeper than he had imagined.