Butterfly Kanae rubbed her eyes in disbelief. But the figure before her was real—it was truly Yōsuke, the person she had long yearned for. Tears streamed uncontrollably down her cheeks as she threw her arms around him, clinging tightly to his body.
"Master… I've missed you so much."
Yōsuke gently patted Kanae's back. "That's enough, don't cry. I've been thinking about you all this time as well."
Tanjirō was stunned. The same Kanae who had appeared so steadfast, kind, and strong—protecting him and Nezuko at Mount Natagumo, and again at the Pillar Meeting—was now weeping like a child in Yōsuke's arms.
The sight stirred memories of his once-happy family. There was a time when he too could lean into his parents' embrace without restraint. Now… Tanjirō felt his nose sting with the urge to cry.
"I'll go call Shinobu and Kanao right away!" Kanae quickly wiped her tears and rushed off to find her younger sisters.
Yōsuke shook his head helplessly. "To think the ever-composed Kanae could be this impatient."
"Yōsuke-san, it's good to see you again," Tanjirō greeted politely.
"Tanjirō, you've done well. I didn't expect that you and Nezuko would defeat Lower Rank Five on your own." Yōsuke reached out, ruffling Tanjirō's crimson hair. The warmth of his hand was so comforting that Tanjirō almost wished to bask in it longer.
"It was only thanks to the blood you entrusted to Nezuko. Without it, I might have died back there." Even now, the memory of Mount Natagumo sent a chill through Tanjirō's heart.
"Don't belittle yourself. Without your and Nezuko's own strength and determination, no amount of my blood would have made a difference."
Seeing Tanjirō's nervous expression, Yōsuke chuckled. "What is it? Do I make you feel that tense?"
Tanjirō stiffened, blurting mechanically: "N-no!"
"Good. But it's already late—you should rest. Hard work is essential, but proper rest is part of that effort too." Yōsuke advised gently.
Tanjirō bowed deeply, then returned to his room.
Yōsuke glanced down from the roof—and there, beneath the eaves, stood Shinobu and Kanao, staring up at him in shock. Tears welled in both of their eyes.
He leapt down. Before he could say a word, Shinobu rushed forward and embraced him tightly, while Kanao clutched at his sleeve, afraid he might vanish if she let go.
From the shadows, Tamayo and Yushirō emerged. Yōsuke smiled faintly. "Come. Let's talk inside."
Inside the Butterfly Mansion, Yōsuke introduced them:
"This is Lady Tamayo, a physician. She has successfully developed a medicine that restores a demon's sanity, and she is also working on a cure that can turn demons back into humans. The progress is promising."
Kanae and Shinobu looked at the elegant Tamayo in astonishment. As doctors themselves, they knew all too well how impossible such an endeavor should be. They had once attempted something similar, but had achieved nothing.
Tamayo replied with a modest smile. "It was merely good fortune. The key was Nezuko's unique blood, along with the blood of the Twelve Kizuki that Yōsuke and Tanjirō brought me."
Yōsuke then explained his purpose for bringing her here.
"Tamayo is now working on a medicine to weaken Muzan himself. But when it comes to toxicology, she lacks expertise. That's why I've brought her to you. I hope you can work together to create such a drug."
"If there's anything we can do to help, we'll give it our all!" The Butterfly Sisters answered without hesitation. When it concerned Muzan, there was no room for delay.
Yōsuke turned to Kanao, who was still gripping his sleeve, clad in the uniform of the Demon Slayer Corps. "So Kanao has become a Demon Slayer now?"
Kanae sighed softly. "At first, I was against it. But… Kanao learned the Flower Breathing purely from memory. She even went behind Shinobu's and my back to take part in the Final Selection."
Yōsuke smiled. "I see. After witnessing so many people hurt by demons, she found her own will to fight. Her emotions are growing stronger. Isn't that a good thing?"
"Master, should we leave this place?" Shinobu asked. "This is within the Demon Slayer Corps' headquarters. If other slayers were to discover Lady Tamayo, conflict might break out."
"If I asked you to abandon the injured here and walk away, wouldn't you both blame yourselves?" Yōsuke teased lightly.
The sisters faltered. They had trained many in the Demon Slayer Corps' medical corps, but when it came to antidotes against demon venom, only the two of them could formulate effective cures. If they left now, the wounded would be left to die. Their kind hearts couldn't bear that thought, and they had no answer.
Yōsuke smiled. "Enough. Don't torment yourselves. Seeing you both find your ideals and fight for them… I'm proud. I'll go see Ubuyashiki Kagaya. I'm certain he will gladly accept Tamayo."
He rose and departed, leaving the room in silence.
Kanae, Shinobu, Tamayo, and Yushirō, unfamiliar with one another, had little to say. The atmosphere quickly grew awkward.
But Tamayo, calm and graceful, broke the silence by initiating a discussion about medical theory. Soon, the conversation flowed more naturally, the awkwardness dissipating.
At the Ubuyashiki Estate—
Kagaya, who had been resting, suddenly stirred as though sensing something. His sightless eyes opened.
"Yōsuke-san… is that you?"
"It's me," Yōsuke replied warmly. "It seems your spirit is holding up well."
"Thanks to the children of the Corps. And thanks to you too—for saving Muichirō, and for slaying an Upper Rank."
"No need to thank me. It was my responsibility."
"Then… you must have a reason for visiting me now," Kagaya said.
Yōsuke introduced Tamayo, explaining the medicine she had already developed to restore demons' sanity, and the progress of her research toward turning demons back into humans.
"That's wonderful!" Kagaya's frail body trembled with renewed vigor. "If such a medicine can be completed, then so many tragedies may yet be prevented. I will issue orders to the entire Corps—no one will interfere with Lady Tamayo, Kanae, or Shinobu in their work."
"I have more good news," Yōsuke added. "Tanjirō is the inheritor of Yoriichi's will—he has awakened the Breath of the Sun. And Nezuko is special as well. Her blood is the key to the medicine that will turn demons back into humans."
"Marvelous… marvelous…" Kagaya's mind rang with joy as the string of good news overwhelmed him. He repeated the words over and over.
"Rest well, Kagaya. The battle will come again soon. When it does, I hope to see you there."
With that, Yōsuke's figure vanished from the estate.
Kagaya, now invigorated, could no longer sleep. He whispered again and again to himself:
"I must live… to witness Kibutsuji Muzan's death with my own eyes!"
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