The sunlight he could never walk under — that was Muzan's eternal weakness.
In this world, there was no Blue Spider Lily to alter or restore his genes.
If he wanted to survive, he would have to save himself.
That was why he devoted himself to studying medical ninjutsu and perfecting his chakra control — to become a healer strong enough to overcome his own limits.
---
"Director Hara has agreed to let you work as a medical assistant," said Nobibei, his instructor at the Academy. "But only on weekends. You're not allowed to skip class or disrupt your normal studies."
It wasn't an unreasonable condition. Nobibei wanted Muzan to become someone like Konoha's White Fang, a shinobi with both strength and intellect.
Learning medical ninjutsu was encouraged — but not if it risked his academic progress.
After all, if his superiors found out the Academy's director was letting a student neglect training for hospital work, Nobibei would be finished.
Muzan simply nodded. "That's fine. An internship is more than enough."
Nobibei hesitated, then added solemnly, "Muzan, you'd better prepare yourself."
He didn't want to crush the boy's enthusiasm, but the reality of the hospital was far from what he imagined.
"Konoha's hospitals aren't as noble as you think. Medical-nin hold low status here. If not for Lady Tsunade, this village would've never even developed medical ninjutsu."
Muzan already knew that.
The rise of medical ninjutsu had been Tsunade's doing — her reforms during the Second Shinobi World War had changed the village's view of battlefield medicine.
But after the Third Great Shinobi War, when she left the village, the system stagnated.
Few ever followed in her footsteps. Medical-nin required perfect chakra precision — something that took years to master.
For most shinobi, it was easier to spend that time learning a powerful combat jutsu instead.
Among Konoha's renowned ninja, only Tsunade herself could be called a "half-medical-nin" — and her fame came more from her monstrous strength and combat prowess than her healing.
"Thank you for your concern, Nobibei-sensei," Muzan replied with a quiet confidence. "But I believe I can take Konoha's medical ninjutsu to a new level."
---
So his new life began — filled with learning and purpose.
Every weekend, Muzan was the first to arrive at Konoha Hospital.
But his enthusiasm wasn't matched by everyone else.
No doctor wanted a child trailing behind them in the operating room.
If he weren't the son of Sakumo Hatake, the White Fang himself, he would've been kicked out on sight.
Eventually, Director Hara sighed and assigned him to a doctor named An'un Seitei, a mid-level medical-nin known for his precision.
"You can stand there quietly," Seitei said curtly, pointing to a corner of the operating room.
He wasn't thrilled about babysitting the White Fang's kid. But since the director had made the request personally, refusing wasn't an option.
"I'll be performing surgery. Don't speak or interfere."
Muzan said nothing, only nodded.
He knew he was being underestimated — but that was fine.
As the surgery began, Seitei's brow soon glistened with sweat. The patient's wound required delicate suturing, and he focused intently, muttering,
"Blood pack, ready the transfusion…"
Hours later, the operation finally ended.
Seitei leaned back, breathing hard — then blinked when he noticed Muzan standing nearby, hands and clothes spattered with blood, calmly organizing instruments.
"You actually helped with the sutures?" he asked, startled.
When Muzan nodded, Seitei's expression changed completely.
"You've got solid medical knowledge for your age. You'll be my assistant from now on."
—
A true medical-nin wasn't defined by their ninjutsu alone — they needed skill with tools, composure under pressure, and an understanding of anatomy.
On the battlefield, those traits were even more crucial than chakra itself.
Though only a chūnin, Seitei was one of the hospital's top surgeons, and under his guidance, Muzan's progress was rapid.
That entire morning passed in constant work — assisting with surgeries, disinfecting tools, recording patient data.
When they finally paused, Seitei chuckled as he handed Muzan a bento box.
"Not bad, kid. You handled yourself well."
Then he passed him a thick scroll of notes.
"Rest up for now. In the afternoon, try practicing medical ninjutsu. These are the basic techniques. Safe enough for beginners."
The scroll contained detailed instructions for three core medical techniques:
1. Basic Healing Jutsu
2. Chakra Scalpel
3. Hemostasis Technique
Most doctors only learned the first — the simplest of them.
The latter two demanded extraordinary control and endurance.
Even the Chakra Scalpel, though low in chakra cost, required several hours of continuous focus — something most shinobi lacked the stamina for.
---
During his next break, Muzan went behind the hospital to practice.
He caught a small rabbit and began channeling chakra through his hands, stimulating the creature's tissue regeneration.
He quickly understood why so few ever mastered medical techniques.
The precision required was terrifying.
Too little chakra, and the wound reopened.
Too much, and the tissue would heal too fast and tear again.
After several hours of trial and error, he finally managed to mend a clean cut without side effects.
"So that's why there are so few medical-nin," he murmured.
His chakra flowed steadily through his palms, glowing faintly green — gentle, yet potent.
It was a modest success, but it marked a true beginning.
...
From then on, Muzan studied with methodical discipline.
While others played during lunch breaks, he slipped into the hospital library, poring over volumes of cellular and genetic research.
"Lady Tsunade really was a genius…" he whispered one afternoon.
Her writings focused on cellular stimulation — how to accelerate the body's natural recovery through chakra manipulation.
It was groundbreaking, but for Muzan, not enough.
He needed to go deeper — to understand how to alter his very genes.
Still, he couldn't follow Tsunade's exact path.
Her research focused on healing, not transformation.
And worse — the only man who had walked that other path was someone Muzan wanted nothing to do with.
"I'd rather not get involved with that slippery snake," he muttered, referring, of course, to Orochimaru.
In all of Konoha, only Orochimaru had truly advanced the science of genetics.
But Muzan knew too well what kind of man he was — and what kind of interest such a person might take in his mutated blood.
As he was debating the risk, the door burst open.
An'un Seitei stood there, pale and breathless.
"Muzan! Hurry — we've got an emergency operation!"
He grabbed Muzan by the arm and pulled him into the operating room.
The scene inside was chaos.
Dozens of wounded shinobi filled the ward — many bleeding heavily, others on the verge of death. The air was thick with the smell of blood and antiseptic.
"What happened?" Muzan asked.
"You've never seen war, have you?" Seitei muttered grimly.
"A squad was ambushed by Suna-nin during a mission. Heavy casualties."
There was no time for further explanation.
They dove into the operation.
Hours blurred together in a haze of blood, sweat, and chakra.
Doctor after doctor collapsed from exhaustion.
Seitei himself stumbled, hitting the floor hard, gasping.
"I'm out of chakra… damn it! There are still patients waiting to be treated!"
As he cursed his own limits, a calm voice broke through the noise.
"Let me handle it," said Muzan.
"I've already mastered medical ninjutsu."