Infinity Castle.
Wooden rooms floated in impossible directions, scattered like stars in a dream.
The sound of Nakime's biwa echoed through the halls, guiding the arriving Upper Rank demons.
The mournful plucking of strings lingered in the air.
With his hands clasped behind his back, Muzan Kibutsuji stood quietly, his crimson eyes sweeping across the Upper Ranks before him.
"Lord Muzan, long time no see!" Daki cupped her cheeks, staring at Muzan with lovestruck eyes.
Beside her stood the twisted, skeletal figure of Gyutaro. Together, the siblings formed Upper Rank Six.
Muzan ignored Daki's affection entirely and instead shifted his gaze.
"Lord Muzan," Upper Rank Five, Gyokko, emerged from an ornate pot, smiling obsequiously though fear trembled in his expression.
Muzan did not acknowledge him. His attention was clearly fixed on someone else—someone he was anxious to see.
He passed over Upper Rank Four, Hantengu, the trembling old demon, and stopped briefly at Upper Rank Three, Akaza, who bowed respectfully.
"Lord Muzan, are you looking for Young Master Ryuya?"
Upper Rank Two, Doma, giggled as he wrapped an arm around the shoulders of the young demon beside him.
"What a coincidence! Young Master Ryuya is right beside me!"
Muzan narrowed his eyes, ready to lecture Doma for his needless enthusiasm—but the moment his gaze fell on his son, the irritation vanished.
A faint, rare smile touched his lips.
Yes—Ryuya Kibutsuji, his child born from a human mother, a miracle among demons.
The pride of Muzan.
The Son of Demons.
"Kokushibo, how is Ryuya progressing?"
More than the Upper Rank meeting, Muzan cared about his son's growth.
As a demon born with special abilities, Ryuya was the second demon in history capable of using the Demon Slayer Corps' Breathing Techniques, following Kokushibo himself.
Upper Rank One, Kokushibo, dressed in his deep purple samurai attire with his Nichirin blade at his waist, lifted his head.
His six eyes met Muzan's calmly.
"Lord Muzan, Ryuya has fully inherited my teachings. He is a Disciple I am proud of."
Kokushibo then turned his gaze toward his student, giving Doma an unmistakable expression of contempt.
"Young Master Ryuya, congratulations!" Doma smiled brightly, entirely unaware of how irritating he was or how much Ryuya hated him.
In his head, Doma genuinely believed the young prince adored him.
Ryuya's fingers twitched around his Nichirin blade.
He exhaled slowly, suppressing the urge to cut Doma down where he stood.
He couldn't kill Doma while Muzan was watching—that would be a mess.
Ignoring the clingy Upper Rank Two, Ryuya offered Muzan a polite, practiced smile.
"Thank you, Father."
Then he bowed respectfully toward Kokushibo.
"And thank you, Master, for your guidance."
Kokushibo nodded once, disciplined and composed.
Doma, however, beamed, "Oh my, it seems Young Master Ryuya will become an Upper Rank soon! I wonder which position the young master desires?"
"Upper Rank Two seems pretty good," Ryuya smiled.
"…Huh?" Doma's grin froze, and the color drained from his face.
How could he treat Ryuya like a cherished younger brother when Ryuya openly aimed for his position—his life?
Before the tension could snap, Muzan's voice cut through the air.
"Enough. Let us begin the meeting."
Ryuya fell silent, drifting into his thoughts.
He was a transmigrator, trapped in the world of Demon Slayer for sixteen years—reborn as Muzan's biological son.
Because he could use Breathing Techniques, Muzan treasured him, and he became Kokushibo's apprentice.
Even without a position in the Twelve Kizuki, Ryuya's status alone allowed him to walk freely among demons.
"Regarding the extermination of the Hashira of the Demon Slayer Corps throughout the generations," Muzan began, "your performance has been… acceptable."
His tone suddenly shifted—wild and unstable, like someone on a mood swing from hell.
"However!"
Muzan's voice cracked with fury.
"Why—why after so many years—has no one found the Blue Spider Lily?!"
Every Upper Rank except Kokushibo bowed their heads in shame.
Ryuya remained expressionless, hiding a small, amused thought.
What would you do, Muzan, if you learned the Blue Spider Lily only blooms during the day?
Ordinarily, Muzan could hear a demon's inner thoughts.
But Ryuya's Blood Demon Art blocked him completely.
After several minutes of rage and scolding, Muzan realized he would get no answers and moved on.
For demons, there were only two missions that mattered:
Kill members of the Demon Slayer Corps.
Find the Blue Spider Lily.
Ryuya had heard these two goals so many times his ears practically had calluses.
"Lord Muzan, I have good news." Doma lifted a finger and casually stirred the goo inside his skull, hunting for memories.
His white hair shimmered under the castle's ethereal light.
"Ah! There it is. I found it." He grinned.
"It's a Hashira from the Demon Slayer Corps. What a lucky fellow—to become Young Master Ryuya's first target!"
Muzan looked pleased.
It was true—despite decades of training under Kokushibo, Ryuya had never killed a Hashira.
This was indeed a milestone.
"Ryuya, what do you think?"
"I'd be delighted," Ryuya replied, meeting his father's gaze.
He couldn't refuse.
"Good. The meeting is adjourned. Ryuya—I expect results. Do not disappoint me."
Muzan turned and vanished into the shadows.
The oppressive pressure disappeared instantly.
Daki immediately latched onto Ryuya's arm, her soft voice dripping with affection.
"Brother Ryuya~!, why don't you ever come visit me in the Red-Light District? Ume misses you so much~!"
"Is that so? Then I'll come spoil Ume properly next time~"
Ryuya flashed a charming grin and casually patted Daki's shapely butt.
He had always been fond of Daki—clingy, sweet, affectionate, and utterly adorable.
"Then it's a promise~! If you break it, Ume will be mad~!"
Gyokko trembled, "Only Daki dares speak so boldly to Young Master Ryuya…"
Ryuya was the demon Gyokko feared most besides Muzan and Kokushibo.
He desperately wanted to please him—but Ryuya had once mocked his pots as "ugly and asymmetrical," which Gyokko still wasn't over.
"Gyokko, that's called flirting! If you don't understand, don't talk nonsense!" Hantengu squeaked, hiding behind Gyokko's pot.
"Be careful not to anger Young Master Ryuya… he's too terrifying!"
"Brother Ryuya," Akaza said with a grin, "you've gotten much stronger these last few years. I'd like to test your strength sometime."
He waited, tense.
But when Ryuya nodded slightly, Akaza relaxed with visible relief.
"Oh my, it's getting late," Doma interrupted cheerfully. "If we don't hurry, that Hashira might escape, and Lord Muzan will be upset!"
Ryuya understood perfectly.
Disobeying Muzan—even as his son—meant certain death.
He absolutely hated depending on anyone for his life, especially a coward like Muzan.
But for now, he had no choice but to bow his head.
"Master, I will take my leave."
Kokushibo's six eyes softened, just barely, "I await your success."
To Kokushibo—Ryuya's true mentor and the person he respected most—the outcome was obvious.
If it was his disciple, victory was assured.
"Young Miss Nakime," Doma said, "Please teleport Young Master Ryuya and me to the Eternal Paradise Cult."
Instead of plucking her biwa, Nakime turned to the black-clad young demon.
"Young Master Ryuya, is that acceptable?"
"Yes. And Miss Nakime—your biwa playing has improved even more."
"…Truly?" Nakime's expression shimmered, touched by his praise.
"If you'd like, I can play the flute for you later. It's a new skill I learned. I'm sure you'll be satisfied."
Doma's eyes twitched.
The difference in treatment is unfair… she barely even looks at me, but one compliment from Ryuya and she acts like this…
"Then come to my mansion tonight," Ryuya said.
"I'd like to hear Miss Nakime's flute performance in full. But for now—please teleport Doma and me to the Eternal Paradise Cult."
With a light pluck of her strings, Nakime distorted the space around them.
Ryuya and Doma vanished from Infinity Castle.