The room was sealed and silent, lit by the faint glow of medical seals along the walls, pulsing softly in rhythm with the barrier network outside.
The air was thick with the scent of antiseptic and faint ozone.
Nagato lay on the medical platform, upper body bare, his back crisscrossed with deep scars and uneven patches of tissue where black receiver rods had once pierced through.
The tissue around those areas still carried faint traces of foreign chakra corrosion.
Kanae worked beside him, her hands glowing with medical chakra.
Her focus was sharp, Byakugan active as she guided the first batch of Hashirama cells through a narrow tube into the marked channels along Nagato's spine.
Ryusei stood nearby, arms crossed, quietly observing the readings on the seal monitor.
"The spread is steady," Kanae said. "They're responding, but not merging. Good."
"That's what we want," Ryusei replied. "Let them settle first. Regeneration comes later."
The goal wasn't full fusion yet, but slow dispersal.
Each microdose carried cells designed to circulate through the lymphatic and minor chakra networks, restoring his body's reaction speed and chakra conductivity.
They monitored the spread for hours, pausing often to adjust seals and suppress abnormal activity.
Whenever the cells began overreacting, Kanae cooled them with a Yin pulse, stabilizing their rhythm.
By the second day, the blackened scar tissue around Nagato's scars had somewhat faded.
The chakra flow through his back grew stronger, more balanced.
"Circulation almost normal," Kanae noted. "Regeneration factor rising by small increments. Still within limits."
Ryusei gave a short nod. "Good. Keep it gradual. We're not testing his full limits yet."
Konan sat silently near the door, watching with folded arms.
She said little, only stepping forward once to wipe the sweat from Nagato's neck.
By the fourth day, Kanae leaned back slightly, eyes tired but satisfied.
"No rejection. Cells are adapting."
Ryusei glanced at the readings again. "Then it's working. Next phase after recovery, we start marrow stimulation."
Kanae deactivated her Byakugan and stepped away. "He'll survive this batch again."
Ryusei's tone stayed calm. "He'd better. I don't plan to waste Hashirama's cells on anyone who can't."
Konan's eyes flicked to him, but she said nothing.
The seals dimmed as the session ended, leaving only the faint sound of Nagato's steady breathing.
Ryusei understood that their research was still very incomplete, and Nagato was their first real test subject of sorts, whom they were using to perfect their procedure for Kiyomi and Pakura later.
So, it was safer to go very slowly with Nagato first.
The process would for weeks, as they slowly got feedback and tried to use what remained of Nagato's original, non-damaged, and vital Uzumaki tissue and merge it evenly with the compatible material from Hashirama's cells, all over his body, not just the most damaged areas.
If done right, the fusion would gradually heal and restore Nagato's body toward its original state, reversing years of decay, or maybe bring forth something even better than before.
However, such perfect integration would probably take a few months.
...
Three months had passed since Ryusei saved Nagato.
The chances of success back then had been uncertain, but the results spoke for themselves.
Nagato was completely healed.
His body had regenerated, his vitality restored, and his spirit had recovered in the process.
When Ryusei first found him, Nagato's chakra reserves were so low he'd almost decided it wasn't worth the effort.
But now, watching him, Ryusei knew he had made the right call.
"This is what a perfect Sage Body looks like," he thought.
Nagato stood before him, no longer pale or skeletal.
His frame was solid now, his hair a bright, healthy red, his skin smooth and unscarred.
The weak, hollowed figure from before was gone, replaced by something closer to what an Uzumaki descendant of such talent should have been.
Even Konan looked quietly amazed.
The difference was staggering.
When the masked Uchiha had once tried to "help" Nagato, the results had been grotesque, machines and chakra rods draining him daily, even further, until he could barely even blink without them.
What Ryusei had achieved was instead the opposite: a full restoration, stronger even than Nagato had been before Hanzo and Danzo's ambush.
Only his empty eye sockets remained, a reminder of what had been lost.
Ryusei gave a small, amused smile. "Guess you'll have to manage without eyes for now. But with your lineage and your new body, sensing should be second nature. You'll survive."
Konan gave him a flat look at the casual tone, but Nagato didn't seem offended.
Ryusei continued, his tone calm but edged with dry humor. "I'll handle the replacement later. Not Sharingan, not Rinnegan, something cleaner. Byakugan, properly cultivated by our enterprise."
"Once Kanae finishes her next fusion stage, we'll prepare a pair for you. I can't hand you just any random eyes after those Rinnegan, but you'll have to make do with Byakugan for now."
He didn't say it out loud, but he already knew Kanae was nearing the limit of how much her eyes could handle.
When she hit that ceiling soon, the surplus would become Nagato's gain.
For now, it was enough.
The man once trapped between life and death stood whole again, calm and strong, while Ryusei quietly calculated what would come next.
Ryusei knew Nagato's body had fully recovered, but strength was another matter.
Outside the few basic ninjutsu Jiraiya had once taught him, Nagato had relied almost entirely on his pure bloodline talents or the Rinnegan his entire life.
Without it, he simply lacked grounding in the basics.
He was, after all, likely descended from one of the few non-core Uzumaki who survived only because they'd been stationed away from the main clan when it was destroyed.
Whatever talent he had likely didn't come from pure lineage, but from a rare stroke of atavism, luck more than heritage.
So, expecting him to know any true Uzumaki techniques was unrealistic.
Ryusei also didn't have the time to let him spend years relearning the clan's fuinjutsu from the ground up, even with Ashina's guidance.
The world was shifting too fast. He might need Nagato in fighting shape within months, not decades.
That left only one real option, as he had hinted to him before: the Slug Sage Mode.
If Nagato succeeded, Ryusei would gain another powerful ally.
If he failed, it would save Ryusei the risk of trying it himself while still giving him a firsthand observation of the process.
A ruthless calculation, but typical of him.
He looked at Nagato and spoke plainly. "There's one way to reach your old level again. Slug Sage Mode. You have the body for it now, so it's possible. Risky, but worth it."
Nagato listened silently for a few moments before nodding.
He still didn't trust Ryusei completely, but the results were undeniable.
After receiving the same cells that the masked Uchiha and his strange creature partner once had, Nagato knew Ryusei's knowledge wasn't empty talk.
Even if he was being used, it was a use that brought him back to life.
He wanted power again, not for peace this time, but for Konan and for revenge.
To kill the one who had destroyed Amegakure, and to give its people rest at last.
"I'll do it," he said simply.
"Good," Ryusei replied. "We leave in a few days."
As he turned away, his mind was already elsewhere.
Before the trip, he and Kanae would begin the next phase of experiments, applying what they had learned from Nagato's procedure to start the Senju cell integration for Kiyomi and Pakura.