[Infinity Castle]
There he was. Muzan Kibutsuji, disguised as a woman in a black kimono, stands on a floating platform. The five remaining Lower Rank Kizuki stood before him, terrified by the cold aura radiating from their progenitor.
Muzan spoke, "Lower your heads and kneel down. Prostrate yourselves."
"Please forgive us, Master!" Lower Rank 4 gasps.
"Who gave you permission to speak?" Muzan's voice cold as ice. "Do not presume your thoughts are of any worth to me. All you are allowed... is to answer my questions."
He looks down at them with eyes that gleam like plum-red blood, his expression one of utter disgust. "Rui... Lower Rank Five... was killed."
He pauses.
"This is my single question for all of you. Why is it you demons in Lower Ranks are so utterly weak?"
"You shouldn't be satisfied merely being among the twelve kizuki.
That is only the start. You must devour more humans, gain more power.
That is the path to becoming useful to me."
He begins to pace slowly, the sound of his footsteps echoing in the silence. "For over a century, the Upper members of the twelve kizuki have remain unchanged, and it has always been those members who have disposed of the Hashira. Meanwhile... how many times have you been replaced?"
Lower Rank 6, Kamanue, thinks to himself: 'Even if you say that to us... we can't just—'
"You can't just what?" Muzan cuts in, his voice slicing through the air. "Are you complaining about your own incompetence? Are you suggesting my expectations are too high?"
Before Kamanue can speak, Muzan's flesh whip expands instantly, obliterating him into a splatter of gore. The other demons tremble violently, pressing their foreheads into the wood.
"However," Muzan continues, then for a second he stopped mid talk.
---
"Gyokko... Upper Rank Five... has perished."
The remaining Lower Moons freeze in terror. An Upper Rank? Dead?
Muzan closes his eyes, delving into the memories transmitted through the blood. He seeks the moment of Gyokko's death. He needs to see the face of the one who broke the century-long stalemate.
[Inside the Blood Memory]
The vision is hazy, tinted red. Gyokko's body disintegrating. Standing over him is Manjiro Asakura. His dragon tattoo glowing a faint, hot white.
But then, Manjiro stops.
He tilts his head, sensing the connection. Slowly, Manjiro turns, looking directly at the fading point of view, directly into Gyokko's dying eyes. The perspective shifts as Manjiro walks closer, his face filling the vision until he is staring directly at Muzan across time and space.
"Oi. You're watching this, aren't you?"
Muzan, in the Infinity Castle, flinches imperceptibly.
In the memory, Manjiro leans in, his eyes glowing with the heat of the mark. "I will find you. And I will kill you."
Then, Manjiro smiles, a bright, fake, customer-service smile. He gives a small, jaunty wave. "And in case I don't see you... good afternoon, good evening, and good night!"
Manjiro stomps on the eye. The memory cuts to black.
[End of Memory]
Back in the Infinity Castle, a vein bulges violently on Muzan's forehead. The tatami mats beneath him crack under the sudden release of his pressure.
"Impudent..." Muzan whispers, his voice trembling with a mixture of disbelief and rage. "That wretched human... dares to threaten me? Me? The closest being to perfection?!"
He turns his gaze to the remaining Lower Ranks. They are staring at him, sensing his fury.
"What are you looking at?" Muzan hisses. "You find this amusing? You think my anger is a spectacle?"
In a swift, explosive surge, Muzan's flesh whips lash out. Lower Ranks 4, 3, and 2 are slaughtered instantly, their bodies torn apart not for failure of their mission, but simply to vent the Progenitor's irritation. He absorbs their blood, reclaiming the power he wasted on them.
Only Enmu (Lower Rank 1) remains, shivering in ecstasy amidst the carnage. When asked for his last words, he smiles euphorically. "It feels like a dream... to hear the others scream... to die by your hand..."
Muzan pauses. The absolute submission soothes his ego slightly. He stabs a needle-like finger into Enmu's neck, pumping a massive dose of blood into him.
"That's more like it." Muzan says coldly. "I'll give you a generous amount of my blood, although you may not be able to handle its magnitude and die. If you do manage to acclimate, you are certain to become stronger. Then you are to make yourself useful."
"By killing hashira of the demon slayers. If you are able to kill the demon slayer wearing hanafuda earrings, as for the Rumble Hashira forget it. But if you are able to bring him down, I will give you even more of my blood.
---
[The Ubuyashiki Estate — Later That Day]
"For the Mugen Train mission, I have decided to send Tanjiro and the others," Kagaya says, his voice calm. "Might I ask what caused you to recommend him in the first place, Shinobu?"
"Tanjiro has a pure soul and will work diligently toward all his goals," Shinobu replies, her smile pleasant. "The potential he showed exceeded my expectations. And perhaps most importantly of all, he has a clear path in mind in regards to defeating Kibutsuji."
"I am in complete agreement with you on those counts," Kagaya nods.
"On another matter," Shinobu continues, "Tanjiro told me that his father used a form of fire breathing."
"Ah."
"As of now, there's no denying that he still has quite a way to go, but I think that Kyojuro Rengoku, our Flame Hashira, could give him some assistance."
"Fair enough," Kagaya agrees.
---
Just then, the sliding door opens abruptly without a knock. Manjiro Asakura is standing there, looking rumpled, his wheat-blonde hair a mess. He looks like he just woke up from a nap.
He pads into the room, not bothering to kneel, and stops beside Shinobu. He crouches down, invading her personal space to look at her face, his own heavy-lidded eyes unnervingly close.
"Shinobu-chan," he says, his voice soft, "You look exhausted."
"My, Manjiro-kun," she replies, not flinching from his proximity, her smile fixed. "What a strange thing to say. I feel wonderful. Perhaps you are projecting?"
"No, I'm not," he says simply, as if stating the weather. "Your smile is tighter than usual. The corners are at a... 15-degree angle. Yesterday they were at 20. This whole dealing with demon things is exhausting, Shinobu-chan."
He sighs dramatically, leaning back on his heels. "It's all so tiresome . How about we just run away? And we could do a painless double-suicide by the river? Think of the peace."
Shinobu lets out a soft 'ara ara' chuckle. "Run away? And abandon my duties? What a terrible idea, Manjiro-kun. Besides, why by a river? It's so... damp. And what if you fail? You seem to have a habit of that."
Manjiro's eyes narrow just a fraction, a silent hit.
"I have a new wisteria poison," she continues, her voice sweet as ever. "It's much more efficient. It's designed to be painless, you see. For... research. Just a little prick, and then... nothing." She holds up her index finger, as if it were a needle, and gently taps him on the nose. "Would you like to be my first human trial?"
Manjiro recoils dramatically, leaning back and putting a hand over his heart in mock offense. "Shinobu-chan, you wound me! That's so cold! You've completely ruined the romance of it. And here I thought you'd be the perfect partner in crime."
Shinobu shrugs, her smile now genuinely amused for a split second. "Surely you can't be serious."
Manjiro throws his arms up in mock despair. "I am serious. And don't call me Shirley."
"But you should rest, Shinobu," he says, his voice quiet, his eyes showing a sliver of genuine concern. "That smile is a lot of work to maintain. You'll wear yourself out."
Shinobu's smile freezes. Her eyes widened almost imperceptibly.
"...What is it you need, Manjiro-kun?" she asks, her voice losing its polite lilt.
He turns to Kagaya. "Master. About the Mugen Train mission."
Kagaya tilts his head. "Yes, Manjiro?"
"Assign Gyomei as backup."
Shinobu's head snaps up, her smile back in place but stained with confusion. "Gyomei-san? For a mission Rengoku-san is handling? That is... extreme, Manjiro-kun. Do you have a reason?"
Manjiro chuckles softly. "Extreme?"
He tilts his head, thoughtful.
"No. Extreme would be sending only one Hashira…"
"Rengoku-san is… reliable," he says lightly. "Which is precisely the problem."
Shinobu blinks.
"When things go wrong," Manjiro continues, "he'll prioritize everyone else. Passengers. Subordinates. Even the demon."
He looks back at Kagaya.
"He won't prioritize himself... so assign someone who will."
Kagaya considers this, his expression unreadable, then smiles gently. "Your insight has proven... flawless. It shall be done, my child."
Manjiro nods, his duty done. He turns and walks to the sliding door, his steps light and silent. He pauses, his hand on the frame, his back to them.
"Master," Manjiro's voice is low, utterly devoid of emotion. "Mark this down in the Corps' record book."
He pauses, letting the silence settle.
"By the time this new phase of missions is complete... three more Upper Rank demons will be dead."