The sun was about to set when Kanae and Shinobu returned home with Kanao.
Seeing nine unfamiliar figures inside along with Yosuke, the sisters froze.
"Master, who are they?"
Yosuke explained calmly. "They are from the Demon Slayer Corps. They've come for you."
"For us?" the sisters asked in surprise.
Ubuyashiki Kagaya stood up and spoke of his purpose. "We came today first to thank you for saving many of our members, and second, to invite you both to join the Corps."
"Join the Demon Slayer Corps? Sorry, but we have no intention of joining," Shinobu refused without hesitation.
"Please don't be so quick to reject us," Kagaya said gently. "The Corps now has countless wounded from fighting demons, many poisoned and awaiting treatment. Ordinary medicine cannot counteract demon toxins. We desperately need your help."
Kanae and Shinobu turned toward Yosuke, seeking his opinion.
But Yosuke only shook his head. "This is for you two to decide."
After a short discussion, the sisters reached a decision. "We can go to treat the wounded Demon Slayers. But we will not join the Corps."
Though he hadn't gained them as full members, Kagaya was satisfied with this outcome.
"Then that is good enough. Thank you, both of you. It's late, so we will take our leave. Here is a kasugai crow. When you are ready, it will guide you to our headquarters. We look forward to your arrival."
Kagaya bowed to Yosuke. "Yosuke-sama, thank you for your understanding. The Corps also welcomes you, should you ever come."
Leaving behind the crow, Kagaya departed with the Hashira.
After they left, Shinobu asked impatiently, "Master, how did the Corps even find this place?"
"I've been settled here for a long time. It's no surprise they know where I am."
Kanae asked softly, "Master, what do you think about their invitation for us to join?"
Yosuke smiled. "I have no particular thoughts. If you want to go, I'll support you. After all, one day you'll have to step back into human society. If you stay by my side forever, you'll only fall out of step with the world."
Shinobu wrinkled her nose. "That won't happen. We'll always stay with Master."
"Haha, alright. As long as you want to, you can always stay by me. But when do you plan to visit the Corps headquarters?"
"Tomorrow. The sooner we go, the sooner we can come back," Kanae decided firmly.
Yosuke nodded. "Very well. My demon crow will follow you at all times. If anything happens, call it, and I will know immediately."
The next morning, before dawn, the Butterfly sisters prepared everything and set out for Corps headquarters.
Since Kanao preferred following the sisters rather than Yosuke, she accompanied them as well.
Meanwhile, in Muzan Kibutsuji's stronghold—the Infinity Castle—the Twelve Kizuki were summoned to a meeting.
"Nearly a thousand years have passed, and still there is no word of the Blue Spider Lily. Useless trash!"
The demon bearing the mark of Lower Rank Three prostrated himself, trembling. " Muzan-sama, the Demon Slayer Corps has been growing stronger. Because of their interference, the search for the Blue Spider Lily has been delayed—"
Muzan's blank gaze fell upon him. "Did I give you permission to speak?"
The words had barely left his mouth before Lower Rank Three's body exploded, snuffed out in an instant.
The sudden death left the other Lower Moons trembling in terror.
Muzan's cold eyes swept across them. "A mere organization of humans, and yet you are helpless before them?!"
"…Even if you say that…" Lower Rank Six muttered in his heart.
Muzan's brow twitched, veins bulging. "Even if I say that? What then? Go on—say it."
His thoughts exposed, Lower Rank Six shook violently, a chill of doom flooding his body.
Muzan seized him by the throat, eyes blazing with fury. "Well? Say it aloud!"
"Spare me, Muzan-sama! Please, have mercy!" Lower Rank Six begged frantically.
But Muzan ignored his pleas. The blood of the Demon King surged within him, and like Lower Rank Three before him, his body burst apart in a bloody instant.
After witnessing the deaths of Two of their own, the rest of the Lower Moons dared not even think of defiance, let alone speak.
Muzan's voice was filled with cruelty. "From this moment on, all demons are to carry out a full-scale assault on the Demon Slayer Corps!"
"Yes, Muzan-sama!"
His icy gaze bore into them. "I have no patience left. I've waited long enough. This time—you will not disappoint me."
At the sound of the biwa, the Twelve Kizuki vanished from the Infinity Castle.
Half a month passed since the Butterfly sisters had left Yosuke.
When they arrived at the Corps' medical headquarters and saw the state of the wounded, they were utterly shocked.
The beds were filled with Demon Slayers whose bodies were rotting from demonic poison. The toxins ceaselessly gnawed at their wounds. For now, only wisteria extract was used, but it merely suppressed the spread of the poison—it could not cure.
Kanae and Shinobu split their tasks—Shinobu worked on antidotes while Kanae tended to patients. But the sheer number of wounded made it impossible to treat them all.
Kanae summoned Yosuke's demon crow, reporting the situation, before throwing herself back into healing without pause.
At first, they thought they could treat the wounded and return quickly to Yosuke. But demons had gone mad, launching attacks everywhere. The casualties only grew, far surpassing what they had seen when they first arrived.
Even Kanao had joined in to help, but it was still like trying to extinguish a fire with a cup of water.
The stream of injured never stopped. None of them were lightly wounded—missing arms and legs was commonplace. The sisters' hearts grew heavy with grief.
Kanae's voice was tinged with sorrow. "Shinobu, the wounded here… this is the true face of humanity's fight against demons. They are admirable people. With mortal bodies, they face monsters. They are heroes."
Shinobu nodded solemnly. "Yes… Only now do I realize how brutal these battles truly are. It's overwhelming."
Watching patients who had barely recovered stand up again, eager to return to the frontlines and continue slaying demons, Shinobu's expression turned grave, filled with respect.
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