The Devil's Disease

Blister plague, red death, black rot, the curse of decay, bone-melt. These were the names this world used for smallpox, scarlet fever, the bubonic plague, leprosy, and bone tuberculosis, respectively.

In addition, malaria was known as the southern fever, and the cinchona tree was called the Tirun tree. As such, this world often called the diseases I knew by entirely different names.

Once I realized this, the very first thing I did was translate the local medical terminology into terms I actually recognized.

And in the process, I discovered a rather peculiar disease.

The Devil's Disease.

A disease that, far from being cured, only worsened the more divine healing magic was applied. It couldn't be treated with holy spells or medicinal herbs; the only recourse was to pray to the gods. It was the ultimate, unbeatable boss of illnesses in this era.

Immediately upon hearing of it, I had confidently dug through the archives.

It's probably just cancer or some rare genetic disorder, right?

Just as smallpox was the blister plague and the black plague was black rot, I assumed the Devil's Disease was simply another name for a condition I was already familiar with.

But when I compiled every historical record of the Devil's Disease, I was left utterly bewildered.

What in the world is this?

The first historical case I looked at was the story of a certain marquis.

At first, I thought the Devil's Disease was cancer. But the next case was bizarre.

Wait. A fever?

Cancer doesn't typically present with a high fever. Of course, tumor fever exists, but that's a rare symptom usually reserved for stage 4 ‍‍‌‌⁠​​⁠‌​​‍​​‍​‌​⁠‍‌‍⁠⁠‌⁠‌‍‌‍‌‌‌‍⁠​‌​‌​‌‍‌‌‌⁠‍​​‌‍⁠‌‌⁠⁠terminal patients. Spiking a fever over 40 degrees Celsius is exceptionally rare.

In other words, I was looking at a contradictory diagnosis where the Devil's Disease was defined as a "tumor-based illness accompanied by systemic high fever."

The problem was that the symptoms didn't stop there.

There was absolutely no consistency from patient to patient. The records of the Devil's Disease documented almost every conceivable symptom a human body could suffer.

Ever since, I had dedicated my spare time to demystifying the Devil's Disease. It was only recently that I finally found the answer.

"Come to think of it, in the old days, people used to confuse the pustule plague with the curse of decay. Though ‍‍‌‌⁠​​⁠‌​​‍​​‍​‌​⁠‍‌‍⁠⁠‌⁠‌‍‌‍‌‌‌‍⁠​‌​‌​‌‍‌‌‌⁠‍​​‌‍⁠‌‌⁠⁠they were eventually recognized as separate over time."

According to my mentor, centuries ago, people couldn't distinguish between smallpox and leprosy, so they referred to both as the curse of decay.

However, as time passed and the study of healing advanced, the two were revealed to be entirely different ailments. Consequently, smallpox became known as the pustule plague, while leprosy retained the name of the curse of decay.

The moment I heard that historical fact, the truth about my misconception regarding the Devil's Disease clicked.

This was a world with underdeveloped medicine, where every medical standard was defined solely by the efficacy of healing magic.

In such a world, every single disease that worsened instead of being cured by healing magic was lumped together under the umbrella of "the Devil's Disease."

In short, the Devil's Disease was a massive, undifferentiated category containing cancer, autoimmune disorders, genetic diseases, and everything else modern science had yet to classify here.

Naturally, classifying these various "Devil's Diseases" one by one had become my latest obsession...

And now, of all times, Freya is showing symptoms of it?

Freya was exhibiting symptoms that perfectly aligned with this dreaded category.

Should I be glad about this timing, or should I despair?

Looking back at my life, it was always like this. The moment I finished researching and synthesizing quinine at age eight, my father caught malaria. Right after I returned from gaining clinical experience in the Red-Light District, my mother and Freed almost died. And now, just as I'm deep into researching the Devil's Disease, Freya falls ill with it.

Sure, this fits the classic tropes of a misunderstanding-themed novel to a T, but...

I didn't cause this, did I? Right?

It's just impeccable timing on my part, right? It's not like I'm some cartoon detective boy who brings death and disaster wherever he goes, is it? ...Please tell me I'm right.

No, that's not what's important right now.

First, I need to classify this specific strain of the Devil's Disease.

As I recalled, the Devil's Disease wasn't a single illness. Cancer, autoimmune disorders, genetic defects—any disease that resisted divine healing magic fell under this label.

Naturally, to treat a disease, you must first identify it. If I wanted to cure her, I had to pinpoint exactly what was ravaging her body.

Let's organize Freya's symptoms.

High fever, non-blanching erythema, conjunctival injection, dry mucous membranes, splenomegaly. And, crucially, her condition worsened after receiving a Minor Heal.

The mechanism of Minor Heal is the acceleration of cellular regeneration and the boosting of the immune system.

A list of diseases that would be exacerbated by a Minor Heal flashed through my mind.

Cancer, autoimmune diseases, rheumatoid arthritis, anaphylaxis... From those, I filtered out only the conditions capable of producing a fever exceeding 41°C (105.8°F). That alone narrowed down the suspects significantly.

Combining that with her history of frequent colds and the fact that she's a fourteen-year-old girl...

Cytokine Storm. Yes. That was the most likely culprit.

When the immune system fights off pathogens, the body raises its temperature to create a hostile environment for the invaders. Heat-sensitive bacteria and viruses lose their strength in the scorching heat and are systematically wiped out.

—Talk about a cheap tactic!

The brain, which normally keeps a strict limiter on body temperature, temporarily overrides its own safety protocols to let the heat rise.

The problem arises when the immune system, locked in combat with the pathogens, goes completely haywire.

—I am no longer under your control!

Normally, the immune system should only raise the temperature to a reasonable degree. But drunk on its own power, it cranks the heat up without limit. The brain, which should be regulating this, has already disabled its safety switch. The fever climbs unchecked, and eventually, the brain literally cooks itself like a sous-vide steak, resulting in death.

This catastrophic hyperinflammatory response is known as a cytokine storm.

It's like burning down the entire house just to catch a single burglar.

Well, strictly speaking, the actual medical science was far more complex, but that was the gist of it.

And in the middle of this, she was hit with a Minor Heal. No wonder her symptoms flared up so violently.

The pathogens inside Freya's body were likely long dead by now. Between the scorching fever and the double dose of healing magic, they had probably been obliterated without a trace.

But the cost was devastating: her body temperature was now rapidly approaching 42°C (107.6°F). I had to bring her temperature down immediately.

Having reached my conclusion, I turned to the female priest, who was frantically dabbing cold sweat from her brow with a handkerchief.

"Sister."

"Y-Yes!" The priestess flinched, her shoulders tensing.

"Every time you cast Heall, the child's condition worsened. Am I correct?"

"Yes..."

"Then why did you keep casting it?"

The priestess's face drained of color.

"T-That's... because the fever wouldn't break... I thought it was ‍‍‌‌⁠​​⁠‌​​‍​​‍​‌​⁠‍‌‍⁠⁠‌⁠‌‍‌‍‌‌‌‍⁠​‌​‌​‌‍‌‌‌⁠‍​​‌‍⁠‌‌⁠⁠because my Holy Power was insufficient..."

"If your Holy Power is insufficient, the spell simply fails to take effect. It does not produce an adverse reaction."

"...Yes, that is true."

"Then when the patient's condition deteriorated, you should have stopped immediately and summoned a superior. Why did you persist on your own?"

"I am so sorry..."

"Hmm. You should have learned about the Devil's Disease during your training. Are you an apprentice priestess?"

"I... I am a low-rank priestess."

Damn it. This was indeed a dark fantasy world brimming with grim realities. Of all the people to send on a house call, they sent a completely green resident.

Actually, wait. Even in the 21st century, local emergency rooms routinely threw fresh interns into the fire. ...Damn it. No matter the world, the most exhausting, high-risk tasks always fall on the lowest rungs of the ladder.

"It was late at night, and since they heard it was just a simple cold, they sent you on this house call."

"Y-Yes..."

It wasn't that she didn't know about the Devil's Disease. She simply lacked the clinical experience to recall her academic knowledge under pressure. It was a common phenomenon among newly minted residents thrown into real-world practice.

Tsk, tsk. She thought she was just treating a common cold, only to be suddenly confronted with the legendary Devil's Disease. How utterly terrified she must have been.

Her mind was probably a complete blank right now. To use an analogy from my past life, it was like an intern pulling a solo night shift when a patient with a stab wound to the heart is suddenly wheeled in. The patient is suffocating, the attending physician isn't picking up the phone, and when the heart finally stops, the panicked intern just starts performing chest compressions. On a patient with a literal hole in their chest! To make matters worse, the patient is the family member of a high-ranking prosecutor.

Honestly, if I had been in her shoes during my intern days, I would have burst into tears too. Actually, I think I did. Tsk. What an idiot I was back then. It was a miracle I managed to clean up that mess. Come to think of it, the professor who bailed me out of that disaster was the one who dragged me into cardiothoracic surgery in the first place. Why did I fall for it? I should have just gone into radiology and enjoyed a decent work-life balance.

My thoughts were drifting, but the point remained: the low-rank priestess had caused a massive medical disaster. She had failed to recognize that her patient was a noble lady suffering from the Devil's Disease, and had repeatedly cast healing magic on her, drastically worsening her condition.

"Sister."

"I am so sorry! Please forgive me, my lord! I... I still have daughters to raise..."

Ah, so she had daughters. She was a working mother. Judging by the wrinkles on her face, she was up there in years. Yet, the fact that she was still a low-rank priestess meant...

She must have started her training late in life.

Well, that was a common sight in medical school too. There were always older classmates who entered med school well past their thirties.

"I understand."

I calmed the sobbing priestess. As Freya's brother, I wanted to rage and demand answers, but doing so wouldn't change our current reality. Right now, Freya was the absolute priority. And to treat Freya, I needed this priestess.

If an absolute worst-case emergency occurs, I'll have to use her to cast healing magic just to keep Freya alive.

Although the healing magic had exacerbated the cytokine storm, it remained an indispensable tool in a true emergency. Because it boosted not just immunity but also raw vitality and regenerative capacity, it could temporarily stave off multi-organ failure. In fact, the only reason Freya was clinging to life right now was because the healing magic had amplified her life force alongside her rampaging immune system. In essence, this low-rank priestess was Freya's life insurance policy.

"I was wrong... Please, I was so wrong..."

However, she was too hysterical to be of any use as an assistant. I needed to stabilize her mental state first. Perhaps a bit of small talk would ease the tension.

"Calm yourself. You mentioned you have daughters. How old are they?"

"They are fourteen and sixteen... Unlike me, they are both brilliant students and have such sweet personalities. Oh, but my eldest has been going through puberty lately..."

"Yes. Good."

I gently cut off the rambling priestess.

"My younger sister happens to be fourteen as well. If you treat Freya as if she were your own daughter and do your absolute best, we can get through this, can we not?"

"...Please, spare my daughters, I beg of you!"

Wait, how on earth did she interpret that? I meant she should rack her brain and apply everything she had ever learned to save Freya. Did she think I was threatening her daughters' lives if Freya died? I would never do such a thing. ...Though my father certainly might. Hmm. Come to think of it, if anything did happen to Freya, I highly doubted this priestess's family would escape unscathed from our house.

"...Please, calm down. What I mean is, have you not learned any methods to manage the symptoms of a patient with the Devil's Disease?"

The priestess shook her head helplessly. I figured as much. The standard protocol for the Devil's Disease in this world was to leave the patient alone and pray. It was essentially a hospice directive: don't prolong their suffering with divine magic, just let them go. And if they somehow survived? Then their prayers had reached the gods.

I asked just in case, but it seems I don't need to worry about keeping up appearances anymore.

From that moment on, the priestess was demoted to a mere healing totem. I felt slightly guilty for completely disregarding her professional authority, but my sister's life was on the line. I immediately mapped out the treatment plan in my head.

First, I have to suppress her immune system.

The root cause of a cytokine storm is runaway inflammation. Therefore, I had to suppress this inflammatory response. Fortunately, I had the perfect drug for the job.

Steroids... Here they are.

Fortunately, I had steroids in my medical bag. Steroids are powerful anti-inflammatory agents, which I had synthesized by processing pig adrenal glands. However, there was a slight catch: the yield from extracting them was abysmally low. Unlike insulin, steroids aren't stored in large quantities within the body; they are synthesized on demand. Consequently, even if you slaughtered a pig, you would only get a microscopic amount. To put it in perspective, it took crushing roughly one ton of pig adrenal glands to yield a single gram of pure steroid. Because of this agonizingly low yield, steroids were an incredibly precious commodity, and I possessed very little of them.

Just one single-gram vial.

This tiny glass ampoule contained the essence of thousands of pigs. No exaggeration, this single vial represented an expense equivalent to the entire research fund I had donated to my mentor this year.

But...

What am I even hesitating for?

There was no room for hesitation. This was my one and only little sister. Amassing wealth, exploiting misunderstandings to climb the social ladder—all of it was ultimately to ensure my family's happiness. What was the point of hoarding this medicine if I didn't use it now?

I pulled out a syringe. Without delay, I tied a tourniquet around Freya's slender arm. Above the faint blue line of her vein, the single gram of medicine—the distilled essence of a ton of raw material—began to flow slowly into her bloodstream.

Please, hold on.

Normally, one would never administer a full gram of steroids in a single dose. A standard oral tablet for allergy patients is typically 10 milligrams—a mere 0.01 grams. I was injecting a dose a hundred times stronger than that all at once. But there was a clinical reason for this madness.

I have to use steroid pulse therapy.

It was an extreme measure: blasting her system with a massive dose of steroids to forcibly shut down her rampaging immune system. Under normal circumstances, doing this risked triggering cardiac arrest. But right now, saving her brain took absolute precedence.

If her heart stops, I can always have the priestess cast Heall or perform CPR myself.

But if her brain cooked, there was no coming back. I had no choice but to take this gamble.

Over the course of five, ten, fifteen minutes, I slowly pushed the entire gram. Slowly, as slowly as possible, manually regulating the plunger. It was my final, desperate effort to minimize the strain on her heart.

Please...

I withdrew the needle and firmly pressed a clean piece of cloth over the puncture wound on Freya's arm.

"Sister."

"Y-Yes!"

"Bring me towels soaked in cold water. And some boiled, cooled water as well. We must prevent dehydration."

"Right away!"

The priestess, now fully broken in as my assistant, rushed out of the room.

I placed my hand on Freya's forehead. It was still burning hot.

Of course it is.

Steroids weren't magic. Pushing the plunger didn't instantly break a fever. It would take at least two hours, possibly up to four, for the drug to take effect. Rationally, ‍‍‌‌⁠​​⁠‌​​‍​​‍​‌​⁠‍‌‍⁠⁠‌⁠‌‍‌‍‌‌‌‍⁠​‌​‌​‌‍‌‌‌⁠‍​​‌‍⁠‌‌⁠⁠I knew this perfectly well, and yet...

Please...

My mind was consumed by a suffocating anxiety.

Then, Freya's weak voice broke the silence.

"Brother..."

"What is it, Freya?"

"Are you... still there?"

"Yes. I'm right here."

I took my sister's sweat-drenched hand. It was the trembling hand of a fourteen-year-old girl. She was old enough to understand what death was, but far too young to accept it.

"You're going to be fine."

I squeezed her hand firmly.

"Because I'm right here with you."

"..."

"What did I tell you before, when Freed was born and fell ill?"

"...To trust you, Brother."

"That's right."

Hearing my reassurance, the tension in Freya's hand eased slightly.

An hour passed.

41.0°C. No change.

Two hours passed.

40.7°C. A slight drop.

Three hours passed.

41.0°C. It spiked right back up.

Damn it...

The fever refused to break. Was the steroid dosage insufficient? Or was the immune system, supercharged by the healing magic, simply too powerful to suppress?

Clicking my tongue, I issued a new command to the priestess.

"Sister. Do you know how to consecrate holy water?"

"What? Ah, yes. I learned the ritual at the seminary... but without the proper sacred symbols here, it will be difficult to..."

"Then go outside and make it right now. There is a prayer room in the annex; you should be able to do it there."

"Yes! I will be right back!"

The priestess hurriedly left the room.

Having sent her away, I looked down at my shivering sister.

In truth, I had one more card to play besides steroids. The problem was that it was a treatment with absolutely zero clinical data. The thought of performing an untested, unverified procedure on my own family made me hesitate to bring it out.

But... I was out of options.

Tsk.

I was so bold when Freed was born. Why am I turning into such a coward now that she's under my protection?

Get a grip, Julian.

I was the protagonist of a misunderstanding-driven story. The kind of protagonist for whom everything always worked out. And on top of that, I was a genius of black magic, recognized by the Great Sage himself. There was no need to overthink this.

What have I been hesitating for all this time?

It was too late for doubts. Steeling my resolve, I gripped Freya's hand tightly.

Holding both of her hands, I quietly began to weave a spell.

The catalyst would be the steroids coursing through her veins. The grammar of the spell would be a curse. And the symbol of choice would be...

...Forgive me.

The Y-shaped crucifix left behind by the priestess. I claimed it as my catalyst.

O Apostle. If you truly possess the symbolic weight I believe you do...

Then please, allow yourself to be sacrificed once more.

Clasping the crucifix tightly in my hands, I chanted in a low, melodic whisper.

The moment the incantation ended, mana drained rapidly from my body. Just as I began to fear the spell had failed, the brass crucifix in my hands melted away, and Freya's raging fever began to plummet.