"You're a madman…"
Kenichi scratched his head as he looked at the barely-breathing test subject in front of him.
It wasn't like he wanted to torture the guy.
The problem was simple—and cruel:
Right now, this Hyūga bastard was the only person he had who already carried cancer cells.
If Kenichi wanted to turn his crazy idea into a real jutsu, this was the only path.
"Relax," he sighed. "I'm not here to scrape your eyeballs today."
The man's eyes were still bloodshot and raw from the last round. Just looking at them made even Kenichi feel a little tired.
There was one thing he could now confirm for sure:
Yang-natured chakra could stimulate the growth of cancer cells.
But the current lab wasn't anything close to a sterile environment. Once the cells left the body, they died too quickly—temperature changes, contamination, bacteria, who knew.
So if he wanted to keep going, there was only one logical next step:
In vivo experiments.
Inject Yang chakra directly into the subject's body and stimulate the cancer cells from the inside.
Kenichi tapped his pen against the clipboard as he thought aloud.
"First step… I need to pour Yang chakra into the target's body. After that, I need some kind of recognition mechanism—something that lets my chakra 'find' the cancer cells as fast as possible…"
In his mind, this jutsu had two fundamental phases:
Get his chakra into the enemy's body.
Make sure that chakra interacts specifically with cancer cells, not everything else.
The first step was already giving him trouble.
Even though he'd adapted a lot to Hashirama's Sage Body, compressing Yang chakra and pushing it into someone else's system was still hard. He could do it roughly, but not with fine control.
And even if he solved that, there was still the crucial question:
How do you make your chakra "lock on" to cancer cells?
Normal people didn't have clearly-developed tumors like this Hyūga did. Their cancerous cells popped up here and there and were usually eliminated quickly.
Trying to find a few abnormal cells in the sea of normal ones was like trying to pick out a single grain of sand on a beach.
And then there was another problem:
What if the target simply didn't have any cancer cells at all?
"Yeah… this is way too convoluted," Kenichi muttered. "Why am I even trying to find them?"
He clapped his hands together as the answer hit him.
"If it's too hard to hunt for existing cancer cells… why not just create one inside them myself?"
Make one. Grow it. Control where it spreads.
Much easier.
After all, cancer was just a normal cell whose DNA had been damaged and gone off the rails. That could be triggered in… other ways.
For example, carcinogens.
Like the nicotine and other nasties in cigarette smoke.
Smokers' lung cells got assaulted constantly by that junk. If their bodies failed to clear the abnormal cells in time, those could eventually turn into lung cancer.
And the lungs were a very important organ.
If something went wrong there, the body paid for it heavily.
Kenichi's eyes lit up.
He grabbed a cigarette from the table and held it up with a grin.
"Want a smoke?"
The Hyūga glared at him, lips trembling.
He didn't answer. He didn't need to.
Even in his condition, he clearly thought Kenichi was insane.
Like this isn't bad enough and you want me to smoke on top of it?!
Kenichi just shrugged and went to work anyway.
He didn't need the guy to actually smoke. There were… other ways to get what he wanted out of the tobacco.
With the equipment in the lab, it wasn't hard for someone with his basic scientific literacy to extract a concentrated nicotine solution from cigarette tobacco. The exact chemistry wasn't pretty, but it was doable.
"Shame I can't get it into crystal form," he muttered. "Liquid is less convenient."
Even so, it was good enough.
Once he had the solution, he filled a small spray device and walked back to the test subject.
Then, without ceremony, he sprayed a fine mist directly over the man's chest.
"What are you doing?!" the Hyūga rasped, panic creeping into his voice.
He could smell the sharp, bitter scent even through the lab air. Fear of the unknown crawled all over his nerves.
"Don't be so nervous," Kenichi said calmly.
Even applied on skin, some nicotine would be absorbed into the bloodstream. If you injected enough directly into a vein, it could be outright lethal.
Of course, as a toxin, it also meant that a skilled medical-nin with extraction techniques could theoretically pull it back out again.
"Assuming there is a medical-nin nearby," Kenichi said thoughtfully. "If there isn't, well… they'd just have to tough it out, huh?"
His eyes brightened.
That's actually a pretty decent poisoning method.
In his previous world, just the nicotine content from a bunch of cigarettes could be enough to kill an adult if concentrated.
But then he paused.
"This world's shinobi are built stronger than normal humans," he reminded himself. "I'd need actual data before I could say how much is lethal here."
He shook his head and refocused on the main point.
For now, he wasn't aiming to kill. He wanted localized damage—enough stress on cells to push them toward mutation, then hit them with Yang chakra to forcibly accelerate that transformation.
Turning lung tissue into a cancerous nightmare from the inside out.
Theoretically.
The problem, again, was control.
How to make sure the nicotine and chakra interacted specifically with the lungs?
How to balance dose, location, and timing?
That would take a lot of experimentation.
Kenichi glanced at the half-dead Hyūga and sighed.
"Well, if I want you to last long enough for all this, I'd better feed you properly."
He decided to improve the man's meals from now on.
A test subject was a resource. If it died before the research was done, where on earth was he supposed to find another one in this condition?
A week later, Orochimaru finally returned.
He stepped into the lab and stopped.
On the table lay the Hyūga bastard child, pale as paper, breathing in thin, ragged gasps. He looked like he'd been wrung out and left to dry.
If it weren't for the faint life still clinging to him, Orochimaru might have thought Kenichi had already gone too far.
"…What exactly have you done to him?" Orochimaru asked, a glint of amusement in his eyes.
Kenichi scratched his cheek with a slightly embarrassed smile.
"Ehehe… I ran a series of experiments on him. I wanted to figure out how those abnormal cells formed in the first place."
Orochimaru had only been gone eight days, but Kenichi had worked eight days straight.
At first the subject had still cursed him between screams.
By the end, he didn't speak at all—just lay there, eyes empty, like something important had been hollowed out.
Still, it hadn't been for nothing.
In those eight days, Kenichi had managed to achieve one important breakthrough:
He could now inject his Yang chakra into a target's lungs with passable accuracy.
It wasn't yet the deadly, perfect jutsu he envisioned.
But it was a crucial first step.
Author's Note: This is all fictional and dangerous in reality. Do not imitate anything described here.