Unlike Kochou Shinobu, who looked utterly miserable, Himejima Gyomei drank the medicine without so much as a twitch—like it was just water. For a moment, Shinobu almost suspected Nightingale of playing favorites, giving them two entirely different concoctions.
But this level of bitterness was nothing to Gyomei, whose mind and body had been tempered by years of harsh ascetic training. In the original story, he was described as a man who "stood above his flawed flesh with the spirit of living stone."
"It's already late. Whatever else needs saying can wait until tomorrow. Proper rest is the foundation of good health."
"Namu Amida Butsu… I couldn't agree more, Nightingale-san."
Of course, sleeping inside the house wasn't really an option—the extra rooms had all been converted by Nightingale into operating theaters. And with Nightingale's temperament, she'd never let a healthy person come and go from her sterile surgical suite. Thankfully, Shinobu and Gyomei were long accustomed to sleeping outdoors on demon hunts. They could sleep anywhere, even on the bare ground. Still, Nightingale found two blankets for them.
When Nightingale stepped outside, she immediately spotted Afune waiting for her.
"Where's Tasuke?"
She asked offhandedly.
"Tasuke's already asleep. Kids need their rest, after all. But don't worry—he brushed his teeth and washed up just like you said, Nightingale-oneesan."
Afune answered with a smile.
"Personal hygiene is important. Over ninety percent of diseases are caused by poor hygiene. And don't forget, you're a child too."
Nightingale's brows drew together slightly. "Children are always brimming with energy and rarely self-disciplined. That's why someone has to make sure they go to bed and wake up on time."
"I know I'm supposed to be asleep right now… but I was a little worried."
Afune's eyes curved like crescent moons. Her voice and appearance were still childlike, but her tone felt surprisingly mature. "Nightingale-oneesan, you're always so focused on what you believe in, you forget how others feel. If nobody reminded you, you'd end up fighting with the guests again."
"No need to worry about the house or the furniture. If anything happened, I'd restrain them before they could cause too much damage."
"That's not what I'm worried about, Nightingale onee-san…"
Afune stared at Nightingale's expressionless face for a long moment, then let out a helpless sigh.
Afune was much younger than Nightingale, yet she often seemed more perceptive, more attuned to the feelings and thoughts of others.
But Afune didn't mind. The way Nightingale struggled with empathy—her blunt, uncompromising nature—was proof that she'd given everything for the sake of saving lives. It only made Afune respect her more.
If Nightingale were really good at reading the room, she probably never would have become a nurse at all… In those days, no one of any standing ever became a nurse. The work was left to ignorant, rough, drunken women with no training.
Because Nightingale insisted on becoming a nurse, she'd fought bitterly with her parents and sister. Her father, frustrated beyond reason, stormed out with his hunting rifle and his favorite dog. Her mother slapped her several times.
But none of it shook Nightingale's resolve. The very next day, she left home and went to a shelter, studying all sorts of "improper" medical knowledge that highborn society disdained.
That one act of "rebellion" made her the founder of modern nursing and nursing education—she saved countless lives.
"So that explains it… No wonder you've been acting so out of character tonight, Nightingale…"
Kochou Kanae had quietly slipped out of the house, arms crossed as she looked between Nightingale and Afune. "Turns out it was all thanks to Afune."
Afune stuck out her tongue and pulled a cute face at Kanae.
"But seriously—how did you do it?"
Ignoring Nightingale, Kanae came around to stand in front of Afune, her eyes shining with curiosity. "You actually managed to talk Nightingale into changing her mind? I've tried so many times and never succeeded… It's like she just doesn't listen."
"That's not true…"
Afune puffed her cheeks in feigned outrage. "As long as you explain things properly, Nightingale-oneesan will listen."
Are you sure?
Kanae didn't say it, but her skeptical look said it all.
While they talked, Kanae sneaked a guilty glance at the very person they were discussing—only to find Nightingale had already wandered off, apparently not interested in their conversation at all.
To be honest, in some ways, Nightingale was just like that guy obsessed with killing goblins. Neither cared at all what others thought of them, and their thought processes were oddly similar…
Goblin Slayer: Can this be used to kill goblins? No? Useless.
Nightingale: Can this be used to kill germs or save lives? No? Useless.
…
Time slipped by.
Autumn had barely arrived when Nightingale first came to this world. Now, spring was already halfway over.
Shinobu and Gyomei had originally wanted to bring Kanae back to the Demon Slayer Corps, but Nightingale refused.
"You really want to drag a patient who's just had surgery—still weak—through mountains and forests?"
This wasn't the modern era with cars and trains. The Corps' headquarters was hidden deep in the mountains to avoid Kibutsuji Muzan's spies; getting there meant trekking rough trails.
For someone who'd just undergone surgery—especially a respiratory operation—it would be torture.
In a hospital, the medical staff's word is law. And if your healer is not only a medical genius but also deadly in a fight, you'd better listen.
Nightingale: If patients don't follow instructions, I know a bit of martial arts too.
Moved? More like… too scared to move…
Nightingale suggested Kanae stay and recover for a while, and Shinobu and Gyomei readily agreed.
Gyomei, as the Corps' strongest Hashira, had important duties only he could handle, so he didn't even stay a full day before leaving. Shinobu, however, remained behind.
Shinobu was just an ordinary member—not even ranked among the highest, and nowhere near as essential as Gyomei. So she stayed to care for her sister.
Initially, Nightingale estimated Kanae would need a full year of observation before she could be "discharged"—that is, brought back to the Corps.
By "discharged," Nightingale didn't mean ready for battle. Unlike Shinobu and Gyomei, Kanae would only be able to live as an ordinary person after leaving here—she was strictly forbidden from returning to combat. If she ever tried, Nightingale would remind her exactly how she'd once gone toe-to-toe with Goetia.
Still, maybe because Kanae cooperated so well, she reached Nightingale's discharge standard in just over half a year.
Over those six months, Nightingale's priorities slowly shifted… She began teaching medicine to Afune—and to Shinobu as well.
Yes, not just Afune; Nightingale planned to teach Shinobu too.
After all, in the original, Shinobu had exceptional medical skills and even ran the Butterfly Estate's infirmary as the Insect Hashira.
Nightingale was sure Shinobu had talent. Afune was still so young—basic knowledge was fine, but anything too advanced was probably too soon.
Nightingale also knew that Shinobu always fretted over her lack of strength—her inability to behead demons. So Nightingale told her about the original Shinobu's fighting style: crafting poisons from wisteria.
Demons, aside from their weakness to sunlight, were vulnerable to wisteria flowers. The Corps used forests of wisteria to trap demons—like the mountain Tanjiro and the others survived to join the Corps.
In the canon, after Dōma killed Kanae, Shinobu studied medicine and worked to perfect wisteria-based poisons. During the Infinity Castle battle, she injected herself with massive doses of wisteria poison, sacrificing herself so Kanao and Inosuke could kill Dōma.
But things were different now: Kanae hadn't been killed by Dōma—Nightingale had saved her. Whether Shinobu would change her battle style as before, Nightingale didn't know—but she decided to give her a push.
After learning about this new fighting style, Shinobu threw herself into medical study with newfound enthusiasm. She understood that if she wanted her poisons to be more lethal to demons, she needed to master pharmacology and medicine.
As for the idea that her teachings would become a weapon against demons—Nightingale was surprisingly unfazed.
Perhaps it was because, in Nightingale's eyes, demons were no longer beings to be saved. They were more like moving corpses—walking plagues.
She'd even seen people online say that every demon in Kimetsu no Yaiba represents a disease.
Upper Moon Six, Daki and Gyutaro: syphilis—since Daki's human name was Ume, their mother died of "ume," and Gyutaro may have congenital syphilitic teeth.
Upper Moon Five, Gyokko: amoebic dysentery—from unclean water, linked to his fisherman background, and his form resembled diseased intestines.
Upper Moon Four, Hantengu: leprosy—his human self was a thief and a liar (the Japanese word for leprosy sounds like "liar" in English), with symptoms like tumors and swollen eyes.
Upper Moon Three, Akaza: measles—the Japanese pronunciation is similar; his blue tattoos evoke old talismans for warding off disease, and his usual red vest recalls the rash.
Upper Moon Two, Dōma: tuberculosis—his ice causes pulmonary necrosis, and TB was called the "factory girls' disease," fitting Dōma's taste for women.
Upper Moon One, Kokushibou: the Black Death—his name even sounds like the disease; the deadliest plague in history, and in Japan, it's classified as a Category I infectious disease, matching his status.
Finally, Demon King Kibutsuji Muzan: cancer—marked by unchecked growth, transformation, and metastasis, all mirrored in Muzan's abilities and origin as a mutated human cell. His vulnerability to sunlight parallels radiation therapy.
Even the three ways to kill demons—wisteria poison, decapitation, and sunlight—could be seen as metaphors for drug therapy, surgery, and radiological treatment. Demon Marks, Nichirin Blades, and the Transparent World echo immunity, high-temperature sterilization, and X-rays.
Even Nezuko—Tanjiro's sister—represented smallpox, the first disease eradicated by humans, matching her eventual return to humanity.
In other words, Kimetsu no Yaiba's hidden theme was disease and medicine.
Disease (demons) brings tragedy. Humanity (the Corps) resists.
So, for Nightingale, exterminating demons wasn't killing living beings—it was eliminating disease and saving lives.
…
"Yay! I can finally return to the Demon Slayer Corps!"
With Nightingale's permission to be discharged, Kanae was at last free to leave and rejoin the Corps. She could hardly wait to see the adorable girls she'd fostered.
She felt like a kid set free after school; even the sunlight on her face seemed warmer.
"I've had enough of living in a place that always reeks of disinfectant…"
"Really? I actually think disinfectant smells nice."
Hearing her from behind, Kanae turned, eyes deadpan, to stare at Shinobu.
It's over. My little sister's been corrupted by Nightingale… She's already turned into Nightingale's mini-me…
Kanae sobbed inwardly.