Five days later, Kanda District, Tokyo.
A youth who looked ninety percent like Rengoku Kyojuro opened the room door.
"Father, I just found Mother's belongings while packing."
"Ruka's belongings?"
Rengoku Shinjuro, who was maintaining his weapon, looked up. "What is it this time?"
"It's a letter."
"A letter? Let me see."
Rengoku Shinjuro put down his weapon.
Because the previous battle had exposed the location of the Rengoku Residence, Rengoku Shinjuro moved to Kanda after packing his bags.
However, perhaps some special switch was flipped, but after moving to Kanda, he and Senjuro found many of Rengoku Ruka's belongings in their luggage.
Looking at these belongings, Rengoku Shinjuro often recalled the times they spent together, and his originally decadent appearance had changed a lot.
[To Rengoku Shinjuro]
He took the letter from Senjuro's hand.
Looking at the familiar handwriting at the beginning, Rengoku Shinjuro fell silent for a moment before looking down.
[Shinjuro, by the time you see this letter, I will likely no longer be here. ]
[Don't be decadent because of me. The one I like will always be you, the one holding a sword with a confident smile on your face. ]
[After I'm gone, I'll leave Kyojuro and Senjuro in your care. ]
[Kyojuro's personality is exactly like yours when you were young; he'll likely follow the old path of the Rengoku family in the future. ]
[Before he completely grows up to take your place, I hope you can...]
...
"Father?"
Seeing Rengoku Shinjuro suddenly start weeping like a manly man, Rengoku Senjuro, who was observing in secret, felt a bit at a loss.
"What's wrong? Are you feeling unwell?"
"...I'm fine. I just remembered some things from the past."
Rengoku Shinjuro put down the letter, took a deep breath to calm his emotions, and stood up from the floor.
The emotions accumulated from seeing old things and thinking of the person over the past few days completely erupted after seeing his wife's last words.
Like a phoenix rising from the ashes, Rengoku Shinjuro's expression quietly changed.
At this moment, it was as if he had returned to that afternoon years ago, when his wife and two children greeted him after he returned from slaying demons.
Just then, the scene in his vision suddenly changed. His wife, Rengoku Ruka, slowly walked away, and his eldest son, Rengoku Kyojuro, also left.
In the once warm and harmonious family, only his second son, Rengoku Senjuro, remained by his side.
"Sorry, Senjuro."
Looking at his second son standing before him, Rengoku Shinjuro raised his hand to pat the boy's head. "I might have to leave you alone to look after the house."
"Father?" Rengoku Senjuro looked up, somewhat confused. "Where are you going?"
"I'm going to the Demon Slayer Corps to bring your big brother back." Rengoku Shinjuro looked into the distance.
As the sun set, the orange-red twilight view reflected in his eyes through the window.
At this moment, there were only three days left until the final battle Lynn had mentioned.
Considering that traveling to the Demon Slayer Corps would take some time, Rengoku Shinjuro didn't delay any longer.
Changing his clothes and putting on his weapon, he bid farewell to Senjuro and headed towards the Demon Slayer Corps.
However, what Rengoku Shinjuro didn't know was that as soon as he left home, Senjuro, whom he had told not to wander off, went to the next street.
"You're here, Senjuro." Lynn, who was waiting for news, opened the room door.
Inviting Senjuro into the room to sit, he asked.
"How was the effect?"
"It was very successful. Father has already set out."
"Hmm? He's already set out?"
A look of surprise appeared on Lynn's face.
"Although he had asked Rengoku Kyojuro to help forge the suicide note to ignite Rengoku Shinjuro's fighting spirit, wasn't this effect a bit too good?"
Looking at the dozen or so letters addressed to Rengoku Shinjuro nearby, Lynn inexplicably felt like it was over before it even began.
"Brother Lynn, you should head back to the Demon Slayer Corps too."
Rengoku Senjuro's voice rang out again. "According to what you said before, the Ubuyashiki Residence will soon be exposed after Father sets out."
"If we waste too much time here, something unexpected might happen."
"You're right. It is time for me to set out."
Lynn pulled out a map and a stack of talismans from his robe. "Take these with you."
Rengoku Senjuro: "This is...?"
Lynn explained, "After your father leaves, your home won't be safe anymore."
"Those talismans come from someone's Blood Demon Art and can help you hide your presence and conceal your figure."
"After I leave, take these talismans and follow the map's guidance to the Demon Slayer Corps' stronghold."
"I understand."
Rengoku Senjuro nodded.
Accepting the talismans and the map, he bowed to the young man before him.
"Brother Lynn, I'm counting on you to take care of Father and Brother Kyojuro."
...
Infinity Castle.
Nakime opened her eyes, feeling in high spirits.
Rengoku Shinjuro had finally regained his fighting spirit.
To reignite that spirit, she had been utterly exhausted these past few days.
She not only had to control her clones to avoid Rengoku Shinjuro's activity areas and prevent discovery,
but also had to rack her brains to find Rengoku Ruka's mementos and place them in conspicuous spots.
After spending a full five days, she finally succeeded in igniting his fighting spirit and making him take up his blade again.
Duang~!
The crisp sound of a plucked string rang out, and Nakime's figure flickered, appearing deep within the Infinity Castle.
"Lord Muzan, I have succeeded."
"Well done."
Muzan, who had been idling, opened his eyes and immediately understood the course of events through mind reading.
"Call Kokushibo and the others over."
"Yes!"
Nakime plucked the strings again, and soon the remaining three Upper Moons were summoned to the Infinity Castle.
Compared to Hantengu and Akaza, Kokushibo, as Upper Rank One, was somewhat bolder.
Under everyone's gaze, he walked straight up to Muzan and asked with a calm expression,
"Is there something the matter?"
"The final piece of the puzzle has been found."
Muzan rose from his chair, a terrifying aura quietly rising from his body.
"Tonight, we launch a general offensive against the Demon Slayer Corps."
...
Time passed, and night fell.
After half a day of travel, Rengoku Shinjuro returned to the Demon Slayer Corps after a long absence.
Walking along familiar paths, he arrived at the Ubuyashiki Residence and met Ubuyashiki Kagaya.
"It has been a long time, Shinjuro."
Ubuyashiki Kagaya exchanged pleasantries: "How has your health been lately? Is Senjuro well?"
"Everything is fine."
"That is good."
Ubuyashiki Kagaya nodded slightly.
Seeing his demeanor, a hint of confusion appeared on Rengoku Shinjuro's face.
"Master, aren't you going to ask me why I've appeared here?"
"The moment you appeared here with your nichirin blade; the answer was already obvious."
A faint smile appeared on Ubuyashiki Kagaya's face: "Welcome back to the Demon Slayer Corps, Shinjuro."
"Master, I..."
Rengoku Shinjuro hesitated, wanting to say something to him.
However, at that moment, a terrifying aura suddenly enveloped the Ubuyashiki Residence.
"Hmm?"
Rengoku Shinjuro's body stiffened, and his expression instantly became serious.
Though he didn't know what was happening, he felt a terrifying killing intent within this aura.
"Master, please wait here for a moment. I will go outside to check the situation."
"Stay calm, Shinjuro."
Ubuyashiki Kagaya slowly stood up.
Compared to the original story, his body had not yet deteriorated to its limit at this point.
Even without support, he could still walk normally, though his speed was a bit slow.
"Come, let us go meet our guest together."
"Guest?"
"Yes, a guest our Demon Slayer Corps has been painstakingly searching for for hundreds of years."
Ubuyashiki Kagaya raised his hand and pulled open the shoji door in front of him.
In the next instant, the scenery of the courtyard appeared in Rengoku Shinjuro's sight.
At the entrance of the courtyard, a figure wearing a white suit walked slowly toward them.
With his hands in his pockets, his scarlet pupils reflected Ubuyashiki Kagaya's figure, and a terrifying killing intent radiated from him.
"A first meeting, Kibutsuji Muzan."
Ubuyashiki Kagaya smiled: "I am the current head of the Ubuyashiki family, Ubuyashiki Kagaya."
"Truly hideous."
Muzan stopped in his tracks, his gaze sweeping over Ubuyashiki Kagaya's face.
Eroded by the curse, Ubuyashiki Kagaya's face was ruined, looking gruesome and terrifying.
"That even someone like you can serve as the head of the Ubuyashiki Clan... it seems the Ubuyashiki have truly declined."
"Declined? No, you are mistaken."
Ubuyashiki Kagaya countered.
Despite being an ordinary human, he showed no sign of cowardice when facing Muzan directly.
"The Ubuyashiki Clan has never declined."
"After a thousand years, I still inherit the will of the Ubuyashiki Clan."
"Your appearance here at this moment is the very manifestation of our unremitting efforts."
Saying this, Ubuyashiki Kagaya paused and looked toward a nearby corner.
"Lynn, do it."
There's someone else?
Muzan, who hadn't noticed anyone at all, was stunned and instinctively followed Ubuyashiki Kagaya's gaze.
But in the next instant, a dangerous aura came from behind him.
"You're even easier to trick than I imagined."
A flat, mocking voice rang out.
Falling along with it was a slash as fast as lightning.
Ssh—!
A crisp tearing sound echoed.
By the time Muzan reacted, his head was already flying into the air.
Not only that, after Muzan's head was severed, several more figures with talismans attached appeared out of thin air, weapons in hand as they surrounded his body.
Amidst the crisscrossing flashes of blades, Muzan's body was slashed with dozens of wounds. An unknown toxin spread through the wounds into his body, suppressing his regeneration.
"Damn it! You bastards!"
Muzan's head grew back from the stump.
Looking at Tomioka Giyu and the others who radiated the aura of demons and were continuously besieging him,
he had no time for mockery now and hurriedly mobilized the power within his body to try and activate a Blood Demon Art.
However, at that moment, Lynn's figure appeared before him once again.
A blade flashed, and Muzan's limbs were severed.
Simultaneously, the unknown toxin in his body began to spread at an extremely rapid rate.
Affected by Lynn's attack and the toxin, Muzan's body stiffened just as he was about to launch a counterattack, and the Blood Demon Art he had just begun charging was instantly interrupted.
"The toxin is working!"
Noticing this, Kocho Kanae, who was part of the pincer attack, immediately issued a reminder.
Seemingly encouraged, the speed of Tomioka Giyu and the others increased by another thirty percent.
"Damn it! You all deserve to die!"
With his counterattack interrupted, Muzan's expression grew increasingly distorted, and the flames of rage occupied his mind.
He widened his eyes, staring deathly at the black-haired youth not far away.
"I will definitely tear you into a thousand pieces! I'll make you understand the consequences of offending me!!!"
"Don't worry, you won't be able to."
As if guessing what would happen next, Lynn returned his nichirin blade to its sheath.
With a flicker of his figure, he arrived beside Kocho Shinobu, who was carrying several large boxes in a corner.
"Everyone, execute Plan B."
Duang~!
Perhaps in response to Lynn,
the moment his voice fell, the crisp sound of a biwa rang out within the courtyard.
In the next instant, the gate to the Infinity Castle appeared beneath everyone's feet.
...