The world is quiet after the battle.
Not the silence of peace — but the hush after a storm that promises another.
The Swordsmith Village has been evacuated and the survivors are en route to recovery. Tanjiro, Nezuko, Mitsuri, Genya, and Muichiro have been ordered by the Corps to rest at the Butterfly Mansion.
And Sung Jinwoo — despite insisting he didn't need rest — has been brought there as well.
Butterfly Mansion — Midnight
Paper lanterns gently sway along the corridors, spreading the scent of herbs and medicine. The soft hum of cicadas blends with the rhythmic breathing of patients sleeping inside.
Jinwoo sits alone on the open balcony overlooking the garden. Unlike the others, he isn't injured. Not on the surface.
But his thoughts are bleeding.
Muzan. The Accursed Moon. The System wants him dead. But how can I kill something this world itself bends to protect?
A voice interrupts his storm.
"Thinking too loud… is bad for the heart."
Jinwoo glances sideways. Shinobu Kōchō stands with her hands behind her back, smiling gently. Her lavender butterfly haori sways in the wind.
"You've been staring at the same spot for over an hour," she continues. "If you keep ignoring sleep, I'll have to sedate you myself."
Jinwoo doesn't know if she's joking.
"I'm not injured."
Shinobu tilts her head. "That's not what I asked."
Jinwoo looks away. "There's no problem."
"Hmm… I disagree," she says softly. "Your eyes look like someone who has already seen the end of the world."
She sits beside him — close enough that he notices the faint cherry blossom perfume she wears.
"You didn't come from a normal land, did you?" she asks quietly.
"…No."
Shinobu smiles — not afraid, not shocked. Almost relieved.
"I knew it," she whispers. "You're too strong to belong to this era."
Before Jinwoo can reply, footsteps approach.
Mitsuri Kanroji — fully wrapped in blankets from resting — hurries toward them, cheeks puffed like a jealous cat.
"Shinobu-chaan!! W-what are you doing with Jinwoo-san alone in the dark??"
Shinobu giggles. "My, Mitsuri-san, I didn't realize you were keeping watch."
Mitsuri flails dramatically, face red. "I'm NOT jealous!! …but maybe a little!"
Jinwoo scratches his neck awkwardly. He has fought gods — but he has no idea how to survive flirty swordswomen.
Then — the System appears.
A translucent blue window forms in Jinwoo's vision.
Only he can see it.
[New Basic Quest Available]
Objective:
Meet the Leader of the Demon Slayer Corps.
Reward:
Level Up (2X)
Penalty for Failure:
Youll Be Teleported To Penalty Zone
Jinwoo's eyes narrow.
"...I need to go."
Shinobu and Mitsuri blink in confusion.
"What? Where?" Mitsuri asks.
Jinwoo replies vaguely. "Your Master wants to see me."
Shock flashes across their faces.
"Kagaya Ubuyashiki…" Mitsuri whispers.
"Shinobu also Whispers... Oyataka sama!!!"
"If he summons someone," Shinobu adds quietly, "it means something huge is happening."
Mitsuri grabs Jinwoo's sleeve tightly.
"Don't go alone! I'll come with—"
Shinobu gently stops her. "The Master requested him alone."
Mitsuri hesitates… then slowly lets go.
"Please… come back safely."
Jinwoo nods once."I promise."
He steps into a nearby shadow.Darkness swallows him — and he vanishes.
Demon Slayer HQ — The Ubuyashiki Estate
Moonlight rests over a peaceful garden. Sakura petals drift across lantern-lit stone paths.
Kagaya Ubuyashiki sits quietly in the center, frail but dignified. Two attendants kneel behind him.
"Sung Jin-Woo," Kagaya says warmly as Jinwoo appears. "Thank you for coming."
Even without strength in his body, Kagaya has a presence that commands reverence. Jinwoo sits across from him.
Kagaya begins:
"Five hundred years ago… Muzan Kibutsuji was born by mistake. Since then, he has turned countless into demons, slaughtered entire families, and built an empire of fear. We have spent centuries fighting him — and we have failed every time."
Jinwoo listens silently.
"Muzan's only weakness is the sun," Kagaya continues. "We long believed no demon could defy it. But then… Nezuko appeared."
Jinwoo's eyes widen.
"Muzan doesn't just fear her," Kagaya says. "He needs her. She is the one miracle that can lead to the end of this war."
Then Kagaya lifts his head — blind eyes pointed at Jinwoo as if seeing through him.
"And now… the first existence Muzan has ever feared stands before me."
Jinwoo clenches his fists unconsciously.He can feel Muzan's hatred burning across the world.
Kagaya bows. A leader bows to a warrior.
"Sung Jin-Woo. I beg of you — protect Nezuko Kamado."
The request needs no hesitation.
"I will," Jinwoo answers. "Even if I have to kill Muzan myself."
A soft relieved smile spreads across Kagaya's fragile face.
"As expected… the sky sent us a warrior when we needed one most."
Kagaya takes Jinwoo's wrist gently.
A symbol ignites on his forearm — a crescent inside a sun, glowing purple and crimson.
The System reacts instantly.
[Title Acquired: SUN-SHADOW MARK]
Effect: Strength ×2 against Muzan + Upper Moons
Kagaya withdraws his hand.
"Only those destined to stand at the end receive this mark."
He exudes serenity, sorrow, hope — all at once.
"The sun rises soon. You must return before the others wake. Not with fear… but with resolve."
Jinwoo rises.
"For their sake. And for Nezuko's."
Soft golden rays seep into the room.
Nezuko sleeps curled beside Tanjiro's bed. Tanjiro weakly opens his eyes — smiling at his sister — then notices Jinwoo entering.
"Jinwoo-san… where did you go…?"
Jinwoo answers calmly — yet his voice contains fire.
"Preparing for the next battle."
Shinobu watches from the hallway — eyes widening as she sees the glowing mark.
Mitsuri rushes into the room.
"You're back—!! I was so scared—"
She freezes when she sees the mark.
"…What is that…?"
Jinwoo looks at all of them — the future pillars of this world.
"It means the next war is near."
Tanjiro clenches his fists.
"Then we'll fight with you!"
Jinwoo shakes his head.
"No. Not yet. For now… rest. Heal. Live."
Nezuko sleepily looks up and smiles at Jinwoo — unaware that the fate of the world hangs on her existence.
The System flashes one final message — unseen by anyone else.
[Main Quest Activated]
Objective:
Erase Muzan Kibutsuji from this world.
Time Limit:
Until the sun sets on the final day.
Jinwoo closes his eyes — shoulders heavy, heart blazing.
I swore I'd protect my sister once.I won't fail this sister now.