Demon Slayer HQ – Medical Wing – Afternoon
The scent of blood and disinfectant lingered in the air.
Shinobu Kocho, the Insect Hashira, stood hunched over a twisted slab of what once was a demon—not theirs, but a Hellspawn. Its flesh bubbled unnaturally, even long after death. Black ichor leaked from its veins. Its tissue refused to decay. Even fire hadn't reduced it to ash.
"Fascinating…" she whispered. "These demons… don't follow biological law."
That's when she heard him.
A quiet knock.
Footsteps… smooth and unsettling.
Muzan Kibutsuji, dressed in white, stood at the doorway of the lab, as if he belonged there.
"Kocho Shinobu," he said softly.
Shinobu didn't turn. "You're not allowed here alone. You're still under restriction."
"I came… with a request."
He stepped forward, his pale eyes lingering on the Hellspawn's corpse.
"You've been studying them. You've seen it too, haven't you?"
"They don't burn in sunlight."
Shinobu stiffened.
"I've noticed," she said coolly.
Muzan's tone sharpened ever so slightly.
"You are a scientist. A curious one. I know curiosity when I see it."
"If we can extract whatever makes these demons invincible to the sun, it can be refined—repurposed. I know you're capable of it."
"And imagine this—demons no longer chained to the night. Fighting alongside your slayers in broad daylight."
Shinobu narrowed her eyes, finally turning.
"Or just… walking the Earth unopposed."
"Do not mistake my curiosity for trust, Kibutsuji."
Muzan smiled faintly.
"I'm not asking for trust. Only results."
Later that evening, Kagaya Ubuyashiki summoned Shinobu privately. Word of the proposal had reached him already.
She stood in his garden, quiet, thoughtful.
"You're considering it," he said, not accusing, not commanding.
Shinobu nodded.
"If I understand how these creatures resist the sun… I might also find how to reverse it. To control it. To weaken them."
Kagaya coughed lightly into a cloth—red staining the white.
"Very well. Study it. But under strict watch. Report everything to me… and to the Slayer."
From a distance atop the far wall of the HQ, the Doom Slayer stood, unmoving, like a statue of death.
He had overheard it all.
His fist clenched briefly.
Sun immunity.
Demons walking free.
He didn't care for their politics. But he knew one thing:
"If they misuse what they find… they burn."