Tamayo drew a vial of blood from the man's arm and began the final examination. Success or failure—all depended on this moment.
Butterfly Kanae turned to the man lying on the bed and asked gently,
"Do you remember anything from before?"
At first, the man's eyes were clouded with confusion. But after a while, clarity returned to them.
"My name is Takumi Masatani (OC)," he said slowly. "I remember being attacked by a strange-looking monster… and then everything went blank. Where am I? What happened to me?"
Kanae smiled softly, soothing his unease.
"Don't worry. We're physicians. You fell ill, so you were brought here for treatment. You're safe now."
By then, Tamayo had finished analyzing the man's blood and came over to the Butterfly sisters.
Even though she tried to compose herself, the faint trembling of her body betrayed her excitement.
With a radiant smile, Tamayo announced,
"It's a success! He has completely returned to being human!"
"I have to tell Master right away!" Shinobu exclaimed, and before anyone could stop her, she dashed out of the laboratory to find Yōsuke.
At that moment, Yōsuke was sharing tea with Michikatsu Tsugikuni. Seeing the breathless Shinobu burst in, Yōsuke asked in surprise,
"Shinobu, what's the matter?"
Catching her breath, she declared,
"Master, we did it! The medicine to turn demons back into humans—it's a success!"
Yōsuke and Michikatsu shot up from their seats with a start, eyes wide in disbelief.
"Truly?" Yōsuke asked again, his voice trembling.
Shinobu nodded firmly.
"It's true! The clinical trial worked. That man has completely reverted from demon to human—his vital signs are no different from any ordinary person's!"
Unable to contain their excitement, Yōsuke and Michikatsu followed Shinobu back to the laboratory.
Inside, the man's restraints had been removed, though his body still looked frail.
Yōsuke and Michikatsu examined him closely.
There were no traces of demonic features, no lingering aura of a demon—he was, beyond any doubt, human once more.
Feeling uneasy under their intense stares, the man asked timidly,
"Um… may I leave now?"
Tamayo smiled kindly.
"Of course. You're completely cured."
The man bowed deeply.
"Thank you so much for treating me. I'll never forget this kindness for the rest of my life."
He departed, but what he left behind was something far greater—a hope for the world.
A way for demons to become human again.
And of all the people who could be happiest about this miracle, there was only one: Kamado Tanjiro.
Upon hearing the news, Tanjiro rushed to the laboratory with Nezuko by his side.
His voice trembled with urgency as he asked,
"Does this mean… Nezuko can really become human again?"
When the Butterfly sisters and Tamayo confirmed it, Tanjiro stood frozen in disbelief.
To let him personally witness this moment of destiny, Kanae handed Tanjiro the syringe containing the medicine.
"Please," she said softly, "you should be the one to do it."
Tanjiro's hands shook as he took the syringe. Memories of that fateful night flooded his mind—the night his family was slaughtered, leaving only him and his sister, turned into a demon.
For her sake, he had taken up the blade.
He had trained until his hands were covered in calluses, fought until his body was torn and battered—yet he had never given up.
Only Tanjiro could truly understand the weight of this moment.
Now that he could finally fulfill his promise to Nezuko and turn her back into a human, Tanjiro found himself somewhat at a loss.
Yosuke patted Tanjiro on the shoulder and encouraged him.
"Tanjiro, everything you've done up to now has been for Nezuko, hasn't it? The time has come—what are you hesitating for?"
Tanjiro replied uneasily,
"It's just... I feel a little lost. If Nezuko regains her memories, how am I supposed to explain everything that's happened to her?"
Yosuke reassured him gently,
"Don't worry. No one here understands Nezuko better than you do. She's kind and gentle—she'll understand everything you've done."
Tanjiro looked down at Nezuko beside him. As if she could sense his confusion, Nezuko reached out and took his hand. In halting, unsteady speech, she murmured,
"O-Onii-chan..."
Tanjiro grasped her hand tightly and nodded firmly. His trembling stopped. With resolve in his eyes, he injected the medicine to turn her human into Nezuko's body.
As the serum entered her bloodstream, Nezuko's body began to sway as if she were drunk. Moments later, she collapsed into Tanjiro's arms, unconscious.
After a thorough examination, Shinobu Kocho gave her diagnosis.
"Nezuko falling asleep is perfectly normal. She's been a demon for a long time—and even one who overcame sunlight. Her blood has become completely different from that of an ordinary demon. However, the medicine is working. Her body's natural defenses have simply forced her into a deep sleep so she can recover her strength."
Tanjiro breathed a sigh of relief.
"As long as she's all right..."
Kanae Kocho then took out two newly prepared doses of the humanization medicine and handed them to Yosuke and Himejima Gyomei.
"Master,Himejima-san—please, the two of you should take it as well."
Yosuke stared at the vial in his hand for a moment before shaking his head and returning it to Kanae.
"Now isn't the time for me to turn back into a human. If I do, I'll lose the strength I need to fight Muzan Kibutsuji. Please keep this medicine safe for me. Once everything is over... then I'll take it."
Gyomei nodded in agreement and handed his own vial back.
"I share Yosuke's thoughts. Now is not the time. When the battle begins, those of us who can fight without fear of injury must stand at the front. Only then can we keep casualties to a minimum."
Kanae sighed helplessly as she accepted the vials.
"Who would've thought... after all the effort we spent developing the medicine, Nezuko would be the only one to use it."
Gyomei's expression grew solemn.
"Muzan Kibutsuji still lives. None of this is over yet. What we can do now is preserve every ounce of our strength for the battle ahead."
At that moment, Tamayo's lips curved into a mischievous smile, as if something amusing had just crossed her mind.
"Tell me—who do you think would be the least willing to turn back into a human?"
Shinobu replied without hesitation,
"Do we even need to guess? It has to be Muzan Kibutsuji!"
Tamayo's smile deepened.
"Exactly. I'm actually looking forward to seeing what he'll be like as a human again. I've developed a number of special compounds designed to weaken him—but they all required a certain precondition to take effect. Now, with the humanization medicine, that condition can finally be met."
At the sight of Tamayo's sly grin, Yosuke and Gyomei exchanged uneasy glances—both feeling a chill run down their spines.