Chapter 18: Kocho Shinobu
Butterfly Mansion.
This was the compounding room in the deepest part of the Butterfly Mansion, a forbidden area where almost no one dared to set foot except for Kocho Shinobu herself.
Kocho Shinobu knelt before the laboratory bench, her back held perfectly straight, a testament to the upbringing and discipline etched into her very bones over the years.
She was dressed in the Demon Slayer Corps uniform, with a butterfly-patterned Haori draped over her shoulders.
In front of her sat dozens of glass vessels of various shapes and sizes.
The ghostly blue flame of an alcohol lamp silently licked the bottom of a flask in the stillness.
The dark purple liquid inside the flask simmered slowly as the temperature rose.
Occasionally, a bubble would surface, letting out a faint "pop" as it burst.
"The age of this wisteria flower seems even better than I expected."
Kocho Shinobu whispered softly, her voice as pleasant as a clear spring in a mountain valley.
She reached out a hand—slender, pale, with a healthy pink hue at the fingertips.
It looked so delicate and frail, as if she couldn't even swing a sword that was slightly heavy.
And that was indeed the case; among the members of the Demon Slayer Corps,
she was the only swordsman unable to decapitate a demon.
But those hands were currently wielding a power far more lethal than a Nichirin Sword.
She gently picked up a long, slender glass dropper.
From a nearby sealed, dark ceramic jar, she carefully drew a single drop of transparent liquid.
It was a neurotoxin extracted from a certain type of venomous insect.
Just one milligram could cause an adult brown bear's heart to stop instantly.
"If I add this, it should accelerate the blood flow, right?
A demon's regenerative ability is troublesome, but as long as the toxin spreads faster than they can regenerate..."
Her gaze was terrifyingly focused, her purple eyes reflecting the simmering purple medicinal liquid in the flask.
She held her breath, her wrist hovering over the flask, steady as a rock.
One drop.
The transparent venom fell, merging into the scalding purple.
In an instant, the previously calm liquid became like an enraged beast.
It boiled violently.
Its color shifted from deep purple to an eerie, fluorescent bright purple.
Then it quickly settled, turning into a deep red that bordered on black.
Finally, it miraculously returned to a clear, translucent pale purple, like the sap of the finest melted amethyst.
A strange, sweet fragrance suddenly exploded within the room.
It was so rich it was almost suffocating, yet it carried a lethal allure.
Kocho Shinobu did not relax immediately; she quickly picked up a glass rod and began stirring clockwise.
The glass rod clinked against the walls of the flask, making a crisp sound.
"The structure of this toxin is very unstable; the temperature must be controlled at sixty-eight degrees.
One degree more and it evaporates; one degree less and it solidifies."
She murmured to herself, a layer of fine sweat beads forming on her forehead and sliding down her smooth cheek.
But she wiped them away with her sleeve before they could fall, completely unbothered.
She couldn't be distracted, not even in the slightest.
For someone like her who lacked physical strength,
this was not just medicine; it was her blade, the foundation of her life in this world filled with demons.
Time slipped away as she stirred.
Finally, the liquid in the flask calmed down completely, showing a near-perfect viscosity and hue.
It refracted a hazy halo under the sunlight, beautiful enough to be intoxicating.
Who could have imagined that this exquisite liquid contained a terrifying power capable of corroding cells and collapsing nerves?
Kocho Shinobu let out a long sigh, her tense shoulders relaxing slightly.
She extinguished the alcohol lamp and gently picked up a sterile test tube, slowly pouring the liquid from the flask into it.
The purple liquid flowed along the tube's wall without a single drop being wasted.
When the last drop fell into the test tube, Kocho Shinobu held it up, scrutinizing it against the sunlight from the window.
"Ah... it really is beautiful."
Her lips curved into her signature smile—gentle, sweet, with the corners of her eyes crinkling slightly.
But if someone familiar with her were present, they might have read a bone-chilling coldness
from those eyes where the smile didn't quite reach.
"Finally, I've succeeded.
This time, I adjusted the concentration of the wisteria and added alkaloids extracted from other flowers.
Theoretically, its destructive power against demon cells should be five times what it was before."
She gently swirled the test tube, watching the liquid cling to the walls
before slowly sliding back down, a near-fanatical scientific gleam flickering in her eyes.
"However..."
Her gaze narrowed slightly, her fingers gently stroking the cool surface of the test tube.
"Theory is only theory, after all.
A demon's physical structure is full of irrational variables.
Without live experimentation, how can I be sure of its true effectiveness?"
She had to test it.
She had to confirm it.
"Then, let's go see that guest."
She carefully placed the test tube into a specially made metal protective case.
Then she took out a pre-sterilized bronze syringe,
filled it with the medicine, and hid it inside her wide sleeve.
She stood up, smoothed out her slightly wrinkled skirt,
and walked out of the room.
Passing through the corridors of the Butterfly Mansion,
Kocho Shinobu's steps did not stop at the infirmary or the courtyard.
Instead, she turned down a dark staircase leading underground.
As the stairs descended, the surrounding air began to grow damp and cold.
The bright sunlight was shut out by thick stone walls, replaced by the dim, flickering light of oil lamps on the walls.
The scent of wisteria in the air gradually faded,
replaced by an inescapable stench of rotting flesh and stale blood.
This was the dark side of the Butterfly Mansion, the only cage in a place meant for healing.
The smile on Kocho Shinobu's face didn't change in the slightest; if anything, it seemed even more radiant against the dark environment.
Her Geta clicked against the stone steps, a crisp "tap, tap"
echoing through the empty underground passage.
At the end was a heavy iron door.
Kocho Shinobu reached out and pushed the door open.
The room was incredibly dim, with only a tiny high-up vent letting in a pitifully weak sliver of light.
In the shadows where that light couldn't reach, a demon was curled in the corner.
He looked utterly miserable.
His limbs were tightly bound by thick, specialized iron chains, the other ends of which were deeply embedded into the stone of the walls.
Not only that, but a collar full of barbs was around his neck,
connected to a beam above his head,
forcing him to keep his head up and preventing any large-scale aggressive movements.
His skin was a sickly bluish-gray,
covered in spots of strange colors and festering wounds.
Those were the marks left by countless previous toxin tests.
Hearing the door open, the demon's dull, glazed eyes snapped wide, and his body began to tremble violently as if struck by lightning.
He saw that figure.
That petite woman in the butterfly-patterned Haori, always wearing a gentle smile.
To the humans outside, she was a goddess who saved lives;
but to this demon, she was an existence more terrifying than Enma in hell.
Kocho Shinobu walked in with light steps.
She closed the door behind her.
"Ara, Mr. Demon, good afternoon."
"Looking at you, you seem quite energetic.
Is it because you knew I was coming, so you were waiting for me?"
Kocho Shinobu tilted her head slightly, the smile in her eyes almost overflowing.
She held her hands behind her back, clutching the syringe filled with purple toxin,
like a girl next door holding candy to coax a child.
The demon's body began to shake violently, and the chains rattled loudly.
A "gurgle" came from his throat, a sign of vocal cord spasms under extreme terror.
"No... no..."
The demon squeezed out a few words with difficulty, his voice hoarse and broken as if he had swallowed two pounds of gravel.
"You... don't come over here..."
"Oh my, that's truly heartbreaking."
Kocho Shinobu feigned surprise, covering her mouth and furrowing her brows in a look of grievance.
"I worked so hard to prepare something delicious for you and came all this way to feed you, and you actually tell me not to come over?
Mr. Demon, being a picky eater isn't a good habit, you know."