Konoha Prison?
Shien glanced questioningly at Uchiha Shizuka, who was leading the way.
Both she and Uchiha Shota were staunch supporters of Mei's faction, so letting her in on a few secrets wasn't a bad thing—it might even prove convenient later.
"You think all those test subjects in Konoha Hospital… where do you think they come from?"
Shizuka's lips curved in a mocking smile.
The Will of Fire?—not even a dog would believe that nonsense.
No matter how prettily it was dressed up, none of the great clans were fooled. Only low-ranking shinobi and a few naive idealists still clung to the Third Hokage's so-called "Will of Fire."
Especially a certain clan leader's son, who had been completely brainwashed by it.
"I see," Shien murmured, finally understanding where the hospital's
"test subjects" originated.
Medical ninjutsu training required practice—lots of it.
At first, trainees practiced on fish. Later, inevitably, on human bodies.
Naturally, they couldn't use ordinary villagers or real patients for that. So the "volunteers" came from the prison—the condemned, who "willingly" offered their bodies for the advancement of medical science.
And that wasn't even counting Root's experiments, which always required a steady supply of human material.
Now it made sense why Shizuka had brought him here.
Konoha Prison provided everything—ample test subjects, safety, and discretion.
As they entered the inner sections, Shien got a good look at the prison's defensive power.
All of the guards were Uchiha.
Several jonin were stationed throughout the facility, and the entire complex was rigged with traps and barriers. Even a Kage-level intruder would find themselves bogged down here.
After winding through the labyrinthine corridors for what felt like forever, they finally stopped before a cell.
"Captain Shizuka!"
A female Uchiha guard standing outside quickly opened the iron door for them.
Shizuka commanded an all-female ninja platoon.
Her official title was Captain of the Fourth Company, First Division of the Konoha Police Force.
The Police Force had four divisions in total. Each division had four companies, each company had four squads, and together with the administrative departments, they formed a self-contained organization—a miniature world unto itself.
Each division's leadership also corresponded to one of the Uchiha clan's main family branches.
Inside the cell, Shien saw a man bound to a metal frame within a barred compartment. His right arm had been severed at the shoulder.
"This one was a rogue ninja we captured recently," Shizuka explained.
"At the moment, he's the only subject who fits your criteria."
A ninja, Shien thought. Perfect.
Using a shinobi for testing was essential.
After all, who could say whether the new Regeneration Serum would behave the same way in a chakra user as it did in a normal human?
That single difference—chakra—made their internal biology worlds apart.
So, if he wanted valid data, he couldn't use an ordinary person.
"No problem," Shien said calmly.
"One subject should be enough."
He didn't expect to need many.
He wasn't worried about whether the serum worked—only about dosage control. That part of the experiment wouldn't require multiple test cases.
Was using people for experiments cruel?
Maybe. But in this twisted ninja world, no one cared.
As long as it wasn't one of their own.
That was the real taboo.
Orochimaru's future betrayal, for instance—his crime wasn't doing human experiments. Every great village did that. No one cared.
The problem was that he'd used Leaf shinobi as test subjects.
Had he experimented only on outsiders, his research would have been quietly tolerated—perhaps even funded.
Now Shien understood perfectly how the shinobi world viewed human experimentation.
As long as you didn't use your own people, it was fine.
That was why Shizuka had brought him here instead of setting up an illegal lab outside the village—it wasn't even considered a big deal.
Shien wasn't about to play saint, either. His only line was that the subject couldn't be innocent.
And this man—an unrepentant murderer of a rogue ninja—was anything but innocent.
He didn't hesitate.
"I'm starting," Shien said as he stepped into the cell.
He carefully injected the serum into the unconscious man's body.
He had asked Shizuka to observe for two reasons—not just to witness the serum's effects, but to serve as his safety net.
If something went wrong, a veteran jonin was enough to handle it.
Shien had no intention of becoming one of those reckless scientists who got torn apart by their own test subjects.
He wasn't Orochimaru—he didn't have Kage-level power or absurd survivability.
Once the injection was complete, Shien stepped back and watched.
Thump… thump…
A deep, rhythmic heartbeat echoed through the cell.
It had begun.
The new Regeneration Serum was taking effect.
The dosage had been carefully calculated—extrapolated from his earlier animal trials and adjusted for human and shinobi physiology.
If the ratio was even slightly off, the result was predictable.
Bang!
The test subject would pop like a balloon.
And the serum wasn't cheap, either.
That single injection had cost nearly ten million ryō—and that was just production cost.
A lab rat's dose used maybe one percent of what he'd just spent on this single tube.
No wonder Orochimaru had later joined forces with Root—the cost of experimentation alone would bankrupt anyone.
"Ahhh!"
"It burns!"
"What's happening to me?!"
The prisoner's screams echoed through the cell, muffled by the thick, soundproof walls.
This was a prison, after all—no one would hear him.
Shien's eyes stayed fixed on the man's right shoulder.
He'd deliberately chosen this subject because of his missing arm.
And now—
Tiny granules of flesh broke through the scar tissue, writhing and knitting together as they began to grow.
It was a grotesque, almost nightmarish sight.
Yet outside the cell, both Shien and Shizuka watched with unblinking anticipation.
Because this scene meant one thing—
The Regeneration Serum worked on shinobi.
Now that the direction was confirmed, all that remained was refinement and replication.
"Pain! It hurts! Somebody help me!"
The prisoner's screams grew louder. His body strained against the bindings, muscles bulging, the ropes creaking.
"Shizuka-san," Shien said evenly,
"make him quiet."
He'd expected pain—it was inevitable. Compressing such massive regenerative power into a brief burst would overwhelm any nervous system.
But he hadn't expected it to exceed the body's tolerance this much.
Even with chakra, the man couldn't endure it.
Step.
Uchiha Shizuka stepped forward, her black pupils flaring crimson.
Three black tomoe spun within her eyes—
The Sharingan.
The Uchiha clan's pride and their most perfect kekkei genkai—versatile, powerful, and capable of evolving through use.
If not for the mental strain it inflicted, it would be flawless.
"Genjutsu: Sharingan!"
Shizuka's gaze locked onto the prisoner, trapping him in illusion.
His convulsions slowed, his screams fading to silence. Only the faint, wet sound of tissue growth remained as new flesh continued to writhe across his shoulder.
Half an hour passed.
The prisoner's missing arm now had a rough, incomplete form—a grotesque mockery of regeneration.
Just as Shien thought they'd succeeded—
Boom!
The man's body suddenly exploded, splattering blood and flesh across the metal bars.
The cell was painted red.
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