Time back to three months ago.
Tokyo, formerly known as Edo, now the heart of the nation, the political center.
Within a certain opulent residence imbued with Western style, a terrifying shadow lurked.
Outside the large floor-to-ceiling windows, the garden plants were trimmed meticulously, forming an elegant landscape with several Western-style sculptures.
Inside, expensive Persian carpets covered the floor. Luxurious yet cold ornaments and paintings were everywhere, showing the wealth of the householder.
This was the residence of Taizo Hirota, the R&D director of Suzuki Pharmaceutical.
The project he oversaw primarily involved the development of plasma preparations, used for adapting to emergency medical treatment on the battlefield or exploration into deeper fields.
And at this moment, he was tutoring his adopted son, Toshikuni from a book, helping him sort out the pharmacological effects of different plants.
Suddenly, Toshikuni, dressed in an exquisite white shirt and outwardly appearing very well-mannered, twitched his brow and stretched a long, lazy yawn: "Yawn...."
"Haha, is Toshikuni sleepy? It's true, we've been studying until late at night. Such a diligent child." Hirota smiled and patted Toshikuni's head, closing the book and putting it away. "Rest well. We'll continue tomorrow."
For Hirota, Toshikuni was the perfect adopted son.
Knowledgeable, kind to others, and especially motivated.
The only pity was that he had a skin condition and couldn't be exposed to sunlight. He could only study at home and had no friends to play with.
Thinking of this, Hirota's gaze grew somewhat deep:
'I need to urge those experimental projects along. We need to develop an effective medicine quickly! I can't have my Toshikuni always unable to see the sun!' He thought.
After he left, Toshikuni gracefully rose from the bedside, straightened his soft black short hair, and stood before the floor-to-ceiling window.
In an instant, his light purple eyes suddenly rolled, revealing scarlet pupils!
A figure appeared miserably before him, dropping heavily to one knee on the thick carpet, one hand still covering his neck.
Upper Rank Three - Akaza.
His powerful body still bore the traces of fierce battle, especially the ferocious wound on his neck.
Even with an Upper Moon's recovery speed, two days later, this fatal wound torn by Taka's burning Nichirin Sword had not yet fully healed.
The edges of the wound showed an unnatural charred black. Dark red demon blood condensed into granulation tissue attempting to suture the wound, but it was resisted by a faint, red-black fighting spirit, making progress extremely slow.
Akaza had thought of simply tearing off this piece of flesh and regenerating it, even if it hurt for a while.
But his combat instinct stirred an unwillingness to admit defeat in him. He wanted to rely on his own recovery power to overcome this suppression, which was why it remained until now.
At the same time, it was a brand of humiliation he had placed upon himself… defeated by another, he must reclaim his honor!
"Akaza." Toshikuni's childlike, crisp voice held not a trace of warmth. It was cold and piercing, like a scalpel scraping glass. "Report."
"Yes, Muzan-sama...."
That's right, the Toshikuni before him was the demon king, Kibutsuji Muzan.
He had once again changed his form, hiding as a human adopted son in a pharmaceutical company, precisely to use these scientists to help him find a way to overcome sunlight.
Muzan himself was extremely cowardly and selfish, unwilling to part with even a sample of his blood, lest someone find his weakness.
When the head of this household's usefulness to him was exhausted, he would not hesitate to completely eliminate him and conceal his existence....
Akaza dared not raise his head. His voice was low as he began to report: "...The Mugen Train mission failed. The Lower Moon, Enmu, was slain. The targets, Kamado Tanjiro and the demon girl Nezuko, were not captured...."
"The reason for failure? Don't make me flip through your mind, Akaza." Muzan said coldly.
"....I encountered the Demon Slayer Corps' Flame Hashira and... a Hashira-level swordsman calling himself Storm.... They were very strong..."
"Very strong? Just two Hashira, what's so strong about them?"
Muzan was genuinely a bit angry. In his view, demons being stronger than humans was only natural.
Not to mention two Hashira, even if all nine Hashira gathered, they were just a bunch of useless rice buckets.
This wasn't the first time he had sent the Demon Slayer Corps fleeing in panic, so he was naturally very dissatisfied with Akaza's performance.
"Tell me, Akaza.... Have you grown too lax?"
"Always going on about pursuing the peak of martial arts. It's been too long since you've tasted enough fresh, life-filled flesh and blood!"
"Have you grown weak? Has your power declined?"
Muzan was about to continue his outburst when he suddenly frowned and noticed Akaza's unnatural way of covering his neck.
He moved his fingers slightly, and Akaza involuntarily released his hand, allowing Muzan to notice the not-yet-fully-healed wound:
"This kind of wound again...." His gaze swept over the strange sensation at Akaza's wound. He reached out and touched it.
'So hot...' His heart skipped a beat, recalling unpleasant memories.
"Muzan-sama... I...." Akaza was about to explain this abnormal wound, but Muzan barked:
"Silence!"
His small form emanated a terrifying aura. His child-like slender hand suddenly grabbed towards the unhealed wound!
Shrrk—!
A tearing sound rang out. Muzan's fingers, like five sharp steel hooks, mercilessly stabbed into Akaza's body, directly grabbing the part of flesh and blood hindering regeneration and viciously tearing it outward!
".....Ugh." Akaza grunted. The fist resting on the ground clenched tightly.
Under Muzan-sama's destructive will, he not only endured the pain of flesh being torn away, but also the shudder originating from his bloodline's source.
But he dared not utter a second cry of pain, only breathing heavily.
In an instant, a bloody, gaping hole was torn in his neck, deep enough to see bone, but it quickly began to heal.
Muzan's small hand pinched the piece of charred black flesh that had been hindering Akaza's regeneration. His pupils contracted slightly.
Beneath the severed tissue and charred black surface, he could feel a faint yet tenacious strange fluctuation...
"This is...." He remembered that when he had devoured Lower Rank Two, Rokuro, there was always an uncomfortable feeling in his stomach, exactly the same fluctuation as this one...
He stopped looking at Akaza and walked directly to a corner of the room, towards an ebony cabinet inlaid with a brass lock.
Opening the cabinet door, inside were neatly arranged various exquisite glass vessels and chemical instruments, practically a miniature laboratory.
He quickly took out a special glass flask, carefully placed the piece of charred black flesh, still lingering with that strange power, into it, and sealed it with a special cork.
Muzan stared at the flask. Deep within his scarlet eyes flickered a cold and dangerous light.
He felt he had discovered an extremely dangerous and highly valuable unknown power....
Relocking the cabinet, when he turned to face Akaza again, the brief surprise on his face had disappeared, restored to that bone-chilling coldness.
Without needing Akaza to say another word, he directly inserted his cold, small finger into Akaza's forehead.
"Let me see... this swordsman who made you so miserable... just what kind of thing he is." Muzan's voice was utterly calm.
Akaza could not resist, could not refuse.
Muzan's will roughly invaded the depths of his mind, rifling through all his memory fragments of the battle on the Mugen Train:
Rengoku Kyojuro.... Flame Breathing.... the boy with the earrings....
Muzan skimmed over these images, finally locking his gaze onto the black-haired boy.
His Nichirin Sword had become as scorching as molten lava, the blade itself humming and trembling from the power it bore...
At the corner of his eye, the ferocious red-black serrated patterns.... like living flames, constantly stinging Muzan's gaze....
Boom—!
A sky-high fear, originating from the deepest part of his soul, spanning centuries, erupted like the most violent volcano in the heart of Muzan!
This scene instantly overlapped with the deepest, most impactful nightmare he could never escape!
The man who had frightened him out of his wits, forcing him to split into one thousand eight hundred pieces just to escape!
The man who had completely knocked him off his pedestal as the exalted, perfect being and cast him into the abyss, forcing him to hide like a stray dog for centuries… the nightmare!
The being whose mere name could freeze the blood in his veins and make him instinctively want to flee desperately—
Tsugikuni Yoriichi!