The moment Muzan Kibutsuji heard Kokushibo's words, he nearly flung the two parasites across the room in shock.
However, in order to preserve his dignity as the progenitor of all demons, he forcibly maintained a calm expression.
"Oh?" Muzan said indifferently, pretending not to care. "Two insignificant insects can consume demons?"
Kokushibo silently raised his right arm.
The bite wound from earlier still remained.
More importantly, it was healing at an abnormally slow rate.
Under ordinary circumstances, even if Kokushibo completely lost an arm, his regeneration would restore it almost instantly. As Upper Rank One, his regenerative capabilities far surpassed those of ordinary demons.
Yet now, the flesh around the wound was regenerating at barely a fraction of its normal speed.
The parasite's saliva was clearly suppressing the regeneration of demon cells.
"…Something is wrong with this substance," Kokushibo said coldly.
Muzan's expression gradually became serious.
Immediately, he used a glass pipette to collect traces of the parasite's saliva from Kokushibo's wound before carefully placing the sample onto a microscope slide.
Not long ago, Muzan had begun studying modern medicine and Western scientific instruments in order to further his research into immortality and resistance to sunlight.
Thus, a newly acquired microscope had already been placed within the Infinity Castle.
After adjusting the lens, Muzan observed the sample carefully.
The deeper he looked, the darker his expression became.
The microorganisms contained within the saliva behaved similarly to phagocytes.
No.
More accurately, they were far more aggressive than normal biological cells.
They devoured everything indiscriminately.
Kokushibo's flesh.
Demon cells.
Even their own surrounding biological material.
The microorganisms consumed and decomposed everything nearby with terrifying efficiency before eventually self-destructing as well.
This was not a characteristic any normal lifeform should possess.
Even Muzan felt a rare sense of unease.
Kokushibo's expression also darkened.
Originally, he had believed Muzan Kibutsuji was the ultimate threat within the world of the Demon Slayer Corps.
Yet now, these unknown organisms had appeared from nowhere.
Worse still, they fed upon both humans and demons alike.
Creatures that stood against both sides simultaneously were far more dangerous than ordinary demons.
Muzan slowly placed the microscope aside.
Although Kokushibo had successfully destroyed the creatures, the mere existence of beings capable of suppressing demon regeneration was already alarming enough.
At present, they were not strong enough to threaten him directly.
But what about later?
What if they evolved further?
What if their numbers increased?
Muzan's instincts immediately urged caution.
The Demon Slayer Corps was already becoming increasingly active, and now strange monsters had begun appearing as well.
Perhaps remaining hidden for another century or two would be the safest choice.
Eventually, all enemies would die of old age.
Muzan had always excelled at patience.
Unfortunately for him, Kokushibo immediately noticed his thoughts.
"…You cannot seriously be considering hiding again."
Kokushibo looked at Muzan speechlessly.
He had already disrupted the Kamado Family's fate, altered numerous future events, and accelerated the world's development.
If Muzan suddenly chose to hide now, then everything Kokushibo had done would become meaningless.
Thus, Kokushibo calmly sat down across from him.
"Lord Muzan," he began slowly, "perhaps these creatures are not specifically targeting demons."
As he spoke, Kokushibo subtly guided the conversation.
Muzan paused.
Indeed.
The parasites consumed humans as well.
That meant demons were not necessarily their sole targets.
Then why had they appeared now of all times?
Kokushibo continued speaking in a deliberate tone.
"Their sudden appearance during this particular era… perhaps it is connected to something else."
He intentionally stopped there.
Rather than explaining directly, he allowed Muzan to arrive at the conclusion himself.
Sure enough, Muzan's eyes gradually widened.
"…The Blue Spider Lily."
The moment those words left his mouth, the obsession within Muzan's eyes became almost frightening.
For over a thousand years, everything he had done revolved around one singular goal:
Conquering the sun.
The Blue Spider Lily represented the key to true perfection.
Once he obtained it, sunlight would no longer threaten him.
At that point, neither the Demon Slayer Corps nor these mysterious parasites would matter anymore.
No matter how strange those creatures were, they would never surpass a perfect lifeform.
Muzan slowly clenched his fist.
Since when had mere insects dared interfere with his evolution?
Although Muzan was extraordinarily cautious by nature, he was also terrifyingly decisive whenever his obsession with immortality was involved.
Otherwise, in the original future, he would never have personally sought out Kamado Nezuko the instant he learned she had conquered sunlight.
The mere possibility of overcoming the sun was enough to override all rational caution.
Now, with the Blue Spider Lily brought back into focus, Muzan immediately abandoned the thought of hiding.
He suddenly looked toward Kokushibo with an unusually serious expression.
"Kokushibo," Muzan said quietly, "I understand that you now possess the ability to resist my commands."
His tone remained calm.
However, this was the first time he had openly acknowledged it.
"Even so, I still hope you will assist me."
Muzan slowly stood.
"Once we obtain the Blue Spider Lily, both of us will finally transcend sunlight together."
Kokushibo was momentarily stunned.
He had never expected Muzan to speak so honestly.
For someone as arrogant and suspicious as Muzan Kibutsuji, openly admitting dependence on another person was practically unimaginable.
Yet the obsession in his eyes was genuine.
To Muzan, overcoming the sun surpassed everything else.
Unfortunately…
Kokushibo himself had absolutely no idea where the Blue Spider Lily actually existed.
Naturally, he neither agreed nor refused.
Muzan also did not force an answer.
After all, openly turning against Kokushibo now would benefit neither of them.
Although Muzan remained stronger overall, Kokushibo had grown far beyond the point where he could be casually controlled.
If the two truly fought, both sides would suffer heavy consequences.
Compared to that, maintaining their current relationship was far more beneficial.
Inside the Infinity Castle, the atmosphere gradually quieted.
Meanwhile, at the Demon Slayer Corps headquarters, an emergency Hashira meeting was already underway.
Ever since repeated encounters involving Upper Rank One had begun occurring, the Hashira gatherings had become increasingly frequent.
In the center of the courtyard lay the dissected remains of the parasite creatures.
The horrifying pile of flesh and bones made even the Hashira uncomfortable.
Kanroji Mitsuri turned pale after one glance before hurriedly covering her mouth and vomiting nearby.
The breakfast she had eaten earlier was completely wasted.
Iguro Obanai immediately stepped forward, gently patting her back while handing her a clean cloth.
Kagaya Ubuyashiki looked toward the gathered Hashira solemnly.
"According to the Corps members who transported these remains," he said softly, "part of the flesh was exposed to sunlight during sunrise."
"It immediately turned to ash."
The Hashira were instantly shocked.
That meant demons had truly existed inside those creatures.
Not merely humans.
Demons as well.
Tokito Muichiro quietly stared at the remains.
For some reason, he could not help wondering whether these monsters were somehow connected to Kokushibo.
After all, bizarre events seemed to appear wherever Upper Rank One became involved.
Sanemi Shinazugawa suddenly grabbed a chunk of flesh from the remains, his expression twisted with disgust.
"Most of this is human meat," he growled. "These things must've been created by demons."
"Maybe Muzan made them himself."
Himejima Gyomei slowly nodded.
That conclusion was understandable.
However, Uzui Tengen crossed his arms thoughtfully before disagreeing.
"Would demons really create monsters capable of surviving under sunlight?"
The question instantly silenced everyone.
Indeed.
If Muzan Kibutsuji truly possessed the ability to overcome sunlight already, then why would he need such creatures?
He would simply emerge personally and slaughter humans openly.
The logic did not fit.
Just as the discussion reached a dead end, Kanzaki Aoi hurried into the courtyard carrying a report.
"The examination results from the Butterfly Mansion have arrived!"
Earlier, another corpse sample had been transported there for Kocho Shinobu and Kocho Kanae to study.
Kagaya accepted the report before instructing his daughters to distribute copies among the Hashira.
As the Hashira read through the findings, their expressions gradually changed.
According to Shinobu's analysis, the creatures were not ordinary insects at all.
Their biological structure existed solely for predation and consumption.
Every cell within their bodies was specialized toward devouring other organisms in order to prolong their own survival.
Even more alarming, the examined bodies were merely outer shells.
The true parasite itself had already been removed from within.
This implied that the actual organisms were significantly smaller.
However, their saliva possessed an extremely powerful suppressive effect against demon regeneration.
The moment Sanemi read that section, his eyes lit up.
"Perfect!" he shouted excitedly. "Then let the demons and these monsters kill each other!"
The other Hashira immediately looked at him helplessly.
Clearly, Sanemi had skipped an important section.
"What?" Sanemi snapped irritably. "Did I say something wrong?"
Tomioka Giyu silently reached over, turned the page in Sanemi's report, and pointed toward the opening paragraph.
"Human flesh is more attractive to them than demon flesh," Giyu explained calmly.
"They digest humans more efficiently."
Sanemi froze.
In other words, humans remained their primary prey.
Demons merely happened to fall within their hunting range.
Kagaya released a quiet sigh.
"It seems the Demon Slayer Corps has gained another responsibility."
His gentle voice echoed through the courtyard.
"From this day onward, we must eliminate not only demons, but these creatures as well."
"The Corps members who encountered them reported hearing the sound 'Manju' repeatedly before the creatures died."
Kagaya slowly raised his head.
"Therefore, let us temporarily designate these organisms as Manju Parasites."
His calm eyes swept across the assembled Hashira.
"The Demon Slayer Corps exists to protect humanity."
"No matter what form evil takes, we shall destroy it."
All nine Hashira immediately straightened.
"Yes, Oyakata-sama!"