(A brief introduction to the world setting; those familiar with the original work can skip this section)
This world is the setting of an anime that Kanzaki Kumo watched in his previous life.
It is a world where humans fight against demons.
The story originated a thousand years ago when an ancestor of the Ubuyashiki Family suffered from a terminal illness in his youth.
A doctor claiming he could cure him came to treat him.
However, after multiple doses of medicine, his condition showed no signs of improvement.
Instead, his body began to undergo strange changes, turning him into a monster.
In a fit of rage, he killed the doctor, halting the unfinished treatment.
Later, that person became powerful and brutal.
Not only did he feel disgusted by human food, but he developed a strong appetite for humans themselves, and the torment of his illness vanished.
If it had only been this, he could have accepted it, but he discovered that he could not bear even a tiny bit of sunlight.
As the legitimate heir of a great clan, he couldn’t even stand under the sun.
He, who already had psychological issues from suffering the illness, completely went mad.
He discovered that devouring humans could make him stronger, and his blood could transform others into kin under his control.
Furthermore, neither he nor the kin transformed by him would age.
Afterward, he named the immortal beings transformed by him ‘demons,’ and he became the King of All Demons, named Kibutsuji Muzan.
From then on, the rampage of the man-eating demons began.
After gaining immense strength and a long life, Muzan had only one goal—to overcome the sun.
From the notes left behind by the doctor he killed, he learned that the final treatment he failed to complete was missing a medicine called the blue spider lily.
If he could obtain it, he could become the truly ‘perfect being’ unafraid of sunlight.
For the next hundred years, Muzan moved about recklessly at night, freely turning people into demons and then ordering those demons to search for the blue spider lily.
The male members died young one after another.
Only by marrying into a family of Shinto priests who served the gods for generations were they able to delay the death of the direct male heirs until the age of thirty, but even that was the absolute limit.
In order to rectify his mistake, lift the family curse, and save all living beings, the Ubuyashiki Family established the Demon Slayer Corps, vowing to fight against demons, with the highest goal of slaying the Demon King.
In the beginning, the Demon Slayer Corps was almost completely suppressed by the demons.
Although the Ubuyashiki Family found minerals containing the power of the sun and cultivated artisans capable of forging those minerals into weapons, humanity was at a massive disadvantage in the long fight against demons.
Even killing the most common demon was extremely difficult.
This was because the nichirin blade, which contained the power of the sun, could only eliminate a demon by severing its neck.
Yet, a human body has more vital points than just the neck.
Demons only needed to protect their necks, while humans had to protect many more areas to maintain their combat effectiveness.
Coupled with the huge difference in physical strength between humans and demons, it made it very difficult for humans to defeat demons.
This situation only began to change with the appearance of that man.
Tsugikuni Yoriichi created a Breathing Technique that could greatly strengthen the human body, fundamentally improving the combat power of the Demon Slayer Corps.
Although the Demon Slayer Corps suffered many casualties afterward, they could at least effectively hunt most evil demons instead of relying on sacrificing human lives as they did in the past.
It was also he who, upon accidentally encountering Kibutsuji Muzan, directly inflicted a lifelong psychological scar, etched into his very genes, upon the Demon King who considered himself invincible.
This caused Muzan to lie dormant for over a hundred years, and even after resurfacing, he acted very discreetly.
One moment of bravery earned a lifetime of cowardice.
During that period of dormancy, Muzan began to truly manage his subordinate forces.
The system known as the Twelve Kizuki was established at that time.
However, Muzan’s so-called management of his forces merely involved creating the Twelve Kizuki, these ‘high-level cattle.’ He bestowed more blood upon the Twelve Kizuki, allowing them to possess greater strength, compelling them to continue searching for the blue spider lily and eliminate the Demon Slayer Corps for him.
At the same time, he forbade his subordinate demons from gathering together.
This was because when he was severely injured by Yoriichi, one demon managed to escape his control while he was weak.
This feeling of losing absolute control over things disgusted and terrified him.
In Kanzaki Kumo’s view, everything the Demon King did, from beginning to end, reflected a clarity untouched by the pollution of knowledge.
It was fundamentally basic.
Despite possessing the means for immortality and overwhelmingly strong power, he never thought of directly approaching those in high positions of power to have them use their influence to search for the blue spider lily.
Wouldn’t that be much faster than him running around the world himself?
After all, if one becomes a demon, they will be controlled by Muzan—if he didn’t say it himself, how would others know?
Even the current Demon Slayer Corps is unclear about the method Muzan uses to control his demons.
The Ubuyashiki Family itself is trying its utmost to seal away any news related to demons, precisely because they fear those powerful figures might develop malicious intentions, don’t they?
Not to mention the various absurd actions Muzan pulled in the original work.
It was no wonder that many people in the world of Kanzaki Kumo’s previous life joked that ‘Muzan’s ‘Wu’ is the ‘Wu’ of incompetence.’
This Demon King, apart from possessing strength unmatched by anyone in the current world, had absolutely nothing praiseworthy about him.
Yet, his strength, fundamentally speaking, owed its existence to that doctor from long ago, and had little to do with Muzan himself.
“No, I can’t keep thinking about this.” Kanzaki Kumo quickly pulled his thoughts back.
If he continued dwelling on it, he would start letting down his guard against Muzan.
Regardless, the current Muzan was an invincible existence in this world, a massive threat to everyone, including Kanzaki Kumo.
Not just Muzan; to the current Kanzaki Kumo, even a random demon was a threat.
Therefore, studying the Breathing Technique well and growing stronger as quickly as possible was the most important thing right now.
Only with sufficiently strong power could he live well in this dangerous world and save those people who had caused him regret in his previous life.
Kanzaki Kumo’s thoughts came to an end.
Just then, the carriage also stopped.
Momoyama.
We have arrived.