Kenji's workshop was a mess.
Medical equipment covered every available surface. Surgical tools lay scattered between syringes filled with strange substances, while monitoring seals quietly tracked vital signs nearby. Stacks of research notes from weeks of animal trials were piled wherever space remained. In the corner, his support puppet stood motionless, ready to assist when needed.
He had been preparing for this moment for months. Before he could take the fight to the Akatsuki, he had to solve a fundamental problem. His missing limbs were holding him back.
The puppet prosthetics he used now were limited. They couldn't channel chakra as efficiently as real flesh and bone. They required constant maintenance. Most importantly, they couldn't keep up with the level of combat he expected against Kage-level opponents.
He needed something that combined the adaptability of living tissue with the enhanced capabilities of his puppet technology.
The scroll Aoi had received from Tsunade lay open on his workbench. Creation Rebirth could regenerate entire limbs by forcing cells to divide rapidly and rebuild damaged tissue. He had studied the technique extensively and conducted dozens of successful trials on animals. The method worked.
But simply regrowing a normal limb wasn't enough. That would only return him to the state he had been in before the injury. Human bones and muscles had limits. What he wanted was biological tissue enhanced with the mechanisms he had perfected through his puppet work.
The problem was figuring out how to make it function.
Kenji removed his left puppet arm and placed it on the workbench. Inside, the mechanisms were sophisticated, including retractable blades, projectile launchers, and sealing matrices designed to store tools and weapons. Years of refinement had gone into making these prosthetics as effective in combat as possible.
Could he incorporate that kind of functionality into living tissue?
He sat down at his workstation and began outlining his approach in a fresh notebook.
First, he needed to confirm that the limb could be regrown at all. The animal trials had been successful, but his own physiology was different. He stripped off his shirt and gripped his left arm at the shoulder joint. With a twist and a pull, the puppet prosthetic came free. He set it aside and looked down at the stump where his real arm had ended years ago.
He glanced at his support puppet. "Ready?"
The puppet nodded.
Kenji closed his eyes and reached out with his chakra, sensing the natural energy around him. He drew it in and filtered it through his body, seeking the balance required for Sage Mode. His chakra surged as his physical abilities sharpened and cellular activity accelerated.
He picked up the first syringe. It contained undiluted Hashirama cells. Previous experiments had shown that the First Hokage's genetic material possessed extraordinary regenerative properties. Unfortunately, it was also violently invasive, constantly trying to overtake and consume normal human cells.
The injection burned as it entered his bloodstream.
His body reacted immediately. Cells at the stump began dividing at a terrifying rate. White growths appeared and spread like roots. His senjutsu chakra pushed back against the invasion, and his Wood Release affinity gave him just enough compatibility to avoid the worst outcome.
Even so, the balance was fragile.
"Four Symbols Seal!"
The support puppet moved quickly. Its hands blurred through seals before pressing against Kenji's torso. The sealing spread across his skin, containing a reserve of life-force chakra he had extracted from defeated enemies using borrowed techniques. The seal began feeding that energy into his system, sustaining the regeneration process.
"Creation Rebirth!"
His chakra surged toward the stump, guided by technique. The Hashirama cells went into overdrive, constructing new tissue at an incredible pace. Bone formed first, followed by muscle, blood vessels, nerves, and skin.
Pain exploded through his shoulder as the limb grew. It wasn't the sharp pain of injury, but a deep crawling burn that came from tissue being forced into existence before it was ready. He gritted his teeth and held the technique steady.
Thirty minutes later, he had a new left arm.
Kenji flexed his fingers. They moved. Sensation was present, though slightly dulled. The arm was pale, its skin carrying the faint off-white tint typical of Hashirama cell influence.
"Good," he said, catching his breath. "Step one complete."
He stood and tested the arm's range of motion. Everything responded as it should. The regeneration had worked.
Then he grasped the new arm at the shoulder and severed it without hesitation.
The limb separated cleanly. Blood flowed for only a moment before Kenji sealed the wound with precise chakra control. He placed the severed arm on the workbench and began examining it.
"Now for the hard part."
Simply regrowing a normal arm would be pointless. What he needed was a limb capable of housing the mechanisms from his puppet prosthetics while remaining biologically alive and fully functional.
The problem was structural. Human bones weren't hollow. Human muscles weren't designed to conceal retractable weapons. The entire internal structure would need to be redesigned.
He retrieved his tools and began dissecting the arm he had just regrown, cutting through skin and muscle until the bone structure beneath was exposed.
Normal human bones were solid and dense, strong enough for ordinary use, but nowhere near as durable as the treated Wood Release timber he used in his puppet limbs.
What if he replaced the bone entirely?
He could generate and shape wood tissue. Wood was lighter than bone and potentially stronger with the right treatment. More importantly, it could be grown hollow, creating internal channels.
He wrote down several notes and sketched out the concept. The plan was to generate bones using Wood Release instead of allowing natural bone growth. Each bone would contain hollow channels running along its length, which could house retractable mechanisms, wire systems, and storage seals. The exterior would then be coated with normal bone cells to preserve durability and maintain proper chakra conductivity.
He prepared for a second attempt. This time he would interfere with the regeneration process and guide it into the structure he wanted. He injected another dose of Hashirama cells and activated Creation Rebirth again.
As the arm began to regenerate, he simultaneously channeled Wood Release. When the skeletal structure started forming, he replaced the natural bone with his own generated material. He shaped the wood to mimic the skeletal structure while leaving hollow channels throughout.
The techniques resisted him. Creation Rebirth attempted to produce normal tissue. Wood Release attempted to grow solid wood. When he tried to merge them, the result became unstable and chaotic.
The arm that formed was badly misshapen.
The bones were uneven. Some areas were far too thick, while others were dangerously thin. Muscle tissue developed irregularly, leaving lumps in some places and gaps in others. The fingers could barely move.
Kenji examined the failure. He severed the malformed arm and dropped it beside the first one.
The problem was trying to do everything at once. He needed a different approach.
Perhaps the limb should be grown in stages. First the skeletal structure using pure Wood Release, then the muscle and tissue added afterward through Creation Rebirth.
He prepared for the third attempt. This time he began with Wood Release alone, carefully constructing a skeletal framework from the stump. He shaped each bone with precision, creating hollow channels and leaving small openings where mechanisms could later be mounted.
The wooden skeleton extending from his shoulder looked strange, but it was exactly what he needed. It was strong, lightweight, and filled with internal space.
Next came the muscle tissue.
He activated Creation Rebirth again. This time he tried to limit the technique so that it generated only soft tissue around the wooden bones.
It failed.
The technique couldn't distinguish the difference. It attempted to grow bone where bone should exist, but found wood instead. The cellular confusion caused the entire process to collapse. The muscle tissue that did form was weak and disconnected, unable to attach properly to the wooden structure.
It was another failure.
He was beginning to understand the real problem. Living tissue and constructed material didn't integrate naturally. His body recognized the Wood Release bones as foreign objects and rejected them, even though the chakra used to create them was his own.
He needed an interface that could trick the body into accepting the artificial skeleton as if it were natural.
The answer came when he reviewed his notes on the Hashirama cells. They were remarkably adaptive and capable of interfacing with almost any tissue type. Perhaps they could serve as a bridge.
A new plan formed in his mind. First, grow the wooden skeletal structure. Next, coat its surface with a thin layer of bone cells cultured from Hashirama cells. Finally, use Creation Rebirth to generate muscle tissue that could attach to that bone layer.
He prepared the cell cultures ahead of time. He grew thin sheets of bone cells in nutrient solutions, which took several days before he had enough material to work with.
This was the fourth attempt.
He constructed the skeleton from Wood Release, shaping it with hollow channels and mounting points. Before adding muscle this time, he manually grafted the cultured bone cells onto the wooden framework. Using medical chakra, he sealed the grafts in place and encouraged the cells to spread across the structure until they formed a continuous coating.
The process took hours. By the end, the wooden bones were fully encased in a thin layer of living bone tissue.
Now came the real test.
He activated Creation Rebirth and directed the technique to develop only soft tissue.
Muscle fibers recognized the bone coating as legitimate skeletal structure and attached properly. Blood vessels spread through the tissue. Nerves extended outward. Skin gradually formed over the surface.
When the regeneration finished, he was holding an arm that appeared almost normal. The skin was pale, but the limb had full range of motion and proper sensation.
However, the hollow channels inside the bones remained empty. He still hadn't solved the problem of integrating internal mechanisms.
He severed the arm to examine it more closely, cutting carefully until the internal structure was exposed.
The wooden bones had maintained their shape perfectly. The bone coating had integrated smoothly. The muscle tissue functioned exactly as intended.
But a new problem had appeared.
The hollow channels had partially filled with bone marrow and connective tissue that had formed spontaneously during the healing process.
He sighed and wrote down the observation.
"The body dislikes empty space. It tries to fill gaps automatically."
He needed to install the mechanisms before the tissue regenerated, or find a way to stop the body from filling the space automatically.
This was the fifth attempt.
This time, he decided to install the mechanisms directly into the wooden skeleton before regenerating the soft tissue around it.
He spent several days preparing, miniaturizing the retractable blades from his old prosthetic, building wire launchers small enough to fit inside the bone channels, and designing storage seals that could be carved directly into the wood without weakening its structure.
The modified skeleton contained several hidden mechanisms. Retractable claws were built into the fingertips. A wire launcher ran through the forearm. And a sealing matrix was carved into the upper arm to store kunai.
Everything was ready.
Kenji attached the mechanical skeleton to his stump and used chakra surgery techniques to connect it to his nervous system. Then he activated Creation Rebirth and focused on regenerating soft tissue around the framework while leaving the internal channels clear.
It was the most delicate chakra control he had ever attempted. Every cubic centimeter of muscle had to be guided carefully so it grew around the mechanisms instead of into them. Blood vessels needed to follow precise routes. Nerves had to be positioned perfectly to preserve full functionality.
Six hours later, drenched in sweat and completely exhausted, Kenji finished.
The arm looked perfect. It moved perfectly. When he focused and sent chakra through the neural connections, the retractable claws slid out from his fingertips.
It was a success.
He tested each mechanism. The wire launcher worked, although the trajectory was slightly off. The sealing matrix activated correctly. The claws extended and retracted without resistance.
There were still problems. The mechanisms didn't channel his chakra as efficiently as he wanted. The wire launcher needed recalibration. The entire arm also felt slightly heavier than it should. The internal mechanisms added weight that threw off his balance.
But those were problems he could solve with further refinement.
Kenji smiled. He had proven the concept.
He cut the arm off once more and began designing the final version. This time he incorporated everything he had learned, refining the chakra channels, repositioning the internal mechanisms, and selecting materials that were both stronger and lighter.
And this time he would replace all three limbs at once. Doing only half the job wasn't good enough.
This time he would do it properly.