Kenji set the glass container aside and reached for the puppet's torso. His fingers found the hidden release mechanism, and the chest panel clicked open.
The interior was nothing like the crude exterior suggested.
Intricate networks of chakra-conductive metal filled the cavity, forming a dense grid that covered every internal surface. Thread-thin wires woven from the same material spread across the puppet's frame in patterns that mimicked the human body's chakra pathway system. He'd studied medical texts extensively to get the layout right, tracing the major and minor pathways, replicating the flow patterns that allowed chakra to circulate through living tissue.
This puppet had consumed nearly all the chakra metal left over from building his prosthetic limbs. He'd started construction back at Supply Point 73, working on it during every spare moment between missions and training. It had taken months of careful crafting to complete. Precision was everything when dealing with chakra-conductive materials. One misaligned connection could disrupt the entire flow network.
Late last night, he'd finally finished the last connections. Now came the real test.
He positioned the glass container next to the open cavity and formed hand seals. His chakra responded immediately, surging through his pathways and gathering in his right palm. A faint blue glow emanated from his hand as he pressed it against the puppet's center mass.
"Seal!"
Chakra poured from his palm into the puppet. A sealing pattern spread across the interior surface, radiating outward. The sealing formula he'd designed was complex. It was actually a fusion of techniques from multiple sources, but the foundation came from Yamanaka clan records, specialized seals meant to interface with their mind-transfer jutsu. He'd supplemented that with higher-level sealing theory purchased from the village archives using all the mission credits he'd accumulated over the past months.
Getting access to sealing scrolls hadn't been difficult. Most ninjas learned at least basic sealing techniques. Even Academy instructors like Iruka knew a few standard formulas. After the Uzumaki clan's destruction, huge amounts of their sealing knowledge had remained in Konoha's possession. As long as you had sufficient merit and weren't trying to access the really dangerous stuff like the Four Symbols Seal or Eight Trigrams Seal used for tailed beasts, the village would let you study whatever you wanted.
The sealing continued spreading, weaving together into a semi-transparent spherical barrier that occupied the puppet's core. When the formation stabilized, he opened the glass container.
The preservative fluid inside was a mixture he'd developed himself, combining standard embalming solution with chakra-reactive compounds. It kept the heart viable while preventing decay. He'd tested multiple formulas before settling on this pale green variant that seemed to maintain the tissue's integrity best.
He poured the heart and fluid into the barrier.
The moment the liquid touched the seal's surface, an invisible force took hold. The heart was drawn inside smoothly, floating to the center of the spherical space where it hung suspended in the greenish fluid. The preservative solution glowed faintly, illuminated by the seal's energy.
He watched the heart beat steadily within its containment. So far, so good. Now for the critical part.
He formed another sequence of hand seals and channeled additional chakra into the barrier. The seal responded by contracting rapidly, compressing the semi-transparent sphere down to the size of an egg. The heart shrank proportionally, still clearly visible through the translucent surface, still beating with that same slow, steady rhythm.
Several thread-like extensions emerged from the barrier's surface, connecting to the chakra-conductive metal pathways he'd built throughout the puppet's body. The links formed smoothly, integrating the sealed heart into the artificial circulation system.
"Finally," he breathed out, pulling his hand back. His chakra reserves had taken a significant hit from the sealing work, but it was done.
The core concept behind this puppet was straightforward in theory but complex in execution. Use ultra-thin, chakra-conductive metal to simulate a human body's chakra pathway system, then install a biological heart as the power source. The heart would generate chakra naturally, just like it did in a living person, and the metal pathways would distribute that chakra throughout the puppet's frame.
A living puppet.
He'd been forced down this experimental path for practical reasons. True mastery of puppet techniques resided in Suna. As a Konoha ninja, he'd never gain access to their advanced methods. But more importantly, he knew from his knowledge of the future that standard puppetry had severe limitations. Even Sasori had only reached Kage-level strength by taking the forbidden route of human puppets, literally converting his own body into a puppet core.
For Kenji, continuing with conventional puppet arts would be a dead end unless he innovated like Sasori had. And frankly, the traditional approach seemed less efficient than just focusing on mastering powerful ninjutsu and becoming a standard jonin.
His External Armor Puppet was useful but still fell within traditional boundaries. It couldn't truly compensate for his combat limitations. This project was different. By combining Yamanaka clan techniques with puppet construction, he was attempting to create something that would truly suit him.
He closed the chest panel and laid the puppet flat on the ground. Time to test if it actually worked.
He formed hand seals again, but this time he wasn't using the Mind Body Switch Technique. That jutsu transferred his entire consciousness into another body, which was powerful but came with a fatal drawback. If the possessed target got injured, his real body suffered the same damage. Not ideal for a puppet that would be fighting on the front lines.
Instead, he was using the Mind Clone Switch Technique.
It functioned similarly to Shadow Clone Jutsu, creating multiple spiritual copies that could each control different targets simultaneously. His main body wouldn't lose consciousness completely, and damage to the controlled targets wouldn't backlash onto him.
The technique had significant drawbacks though. The user's spiritual energy got divided evenly among all clones, leaving each individual clone extremely weak mentally. That meant they could only possess unconscious or non-resistant targets. And because the user's mental power was split, their main body would fall into a brief daze, losing most of their mobility.
But those limitations barely affected him. His spiritual mutation from the transmigration had somehow tripled his mental capacity compared to the original body. As long as he didn't create too many clones, his main consciousness would stay functional.
More importantly, he was possessing a puppet with no self-awareness. There was no mental resistance to overcome, which completely bypassed the issue of weak spiritual clones.
The real advantage was efficiency. His spiritual energy far exceeded his physical energy at this point. Most of his mental capacity sat idle and unused. If he could convert that surplus into combat power through puppets, it would be the key to breaking through the normal limitations of ninja ability.
"Mind Clone Switch Technique!"
A translucent copy of his consciousness emerged from his forehead, streaking like a beam into the puppet. The moment the spiritual clone made contact, faint chakra ripples spread across the puppet's surface.
The puppet's eyes shifted slightly. Its fingers twitched.
"It's working!" Excitement surged through Kenji.
The theory was quite sound. The design was functional. Yamanaka secret techniques and puppet arts could be combined successfully. This proved it.
Then the puppet went completely still.
The brief movements stopped as suddenly as they'd started. The puppet's eyes locked in place, fingers frozen.
"What the hell?"
He crouched down immediately and started examining the puppet. His hands moved quickly, checking connections, and testing the chakra pathways for blockages. Everything looked intact. The metal framework showed no signs of damage. The sealing formula linking the heart to the circulation system was still stable, no breaks in the sealing.
He placed his palm against the puppet's core and extended his chakra senses inward, feeling for the heart's energy output.
There it was. The problem.
"The chakra's too weak."
The puppet was generating chakra, but the output was pathetic. Barely a trickle compared to what it needed to function. Not even close to enough power to drive its mechanisms, let alone perform any kind of combat techniques.
"Release!"
The mind clone dispersed, and his spiritual copy returned to his body. Through the clone's memories, he confirmed what he'd sensed. The puppet was producing energy, but at levels far too low to be useful.
He sat back on his heels. "Where did I screw up?"
He'd modeled the entire design around Kakuzu's technique. The Akatsuki member gained different chakra natures by harvesting hearts from enemies. Five hearts, five elemental attributes, tremendous power. The logic seemed straightforward. Hearts were likely responsible for "producing" chakra, so installing one in a puppet should give it an independent power source.
"Chakra forms from the fusion of physical and spiritual energy," he muttered. "The spiritual energy comes from my mind clone. The physical energy should come from the heart."
He paused.
Something was wrong with that assumption.
"Wait. Physical energy is extracted from cells throughout the body. A single heart doesn't have nearly enough cells to generate significant physical energy. Of course it can't produce enough chakra to sustain consumption."
He'd misunderstood how Kakuzu's technique worked.
"The hearts weren't the power source," he said aloud, pieces clicking together in his mind. "They were attribute filters. The hearts provided different chakra natures, but the actual energy came from the Earth Grudge Fear threads throughout Kakuzu's body. The Earth Grudge Fear was the real source, and the hearts just modified the output."
He wanted to punch himself for the oversight. Kakuzu's body was filled with those black tendrils, an entire secondary system that connected to multiple hearts. The hearts themselves were just components in a much larger mechanism.
A single isolated heart had nowhere near enough biological material to generate combat-level chakra.
"Damn it."
He rubbed his face, feeling the exhaustion from the failed experiment. He'd spent months on this puppet, used up all his remaining chakra metal, and the design was flawed.
But at least the mistake was clear now. This wasn't a total loss.
"The core concept is still valid," he told himself. "Yamanaka techniques combined with puppetry works. The mind clone can possess and control the puppet. The chakra pathway system functions correctly. I just chose the wrong material for the power source."
He stood up and pulled out a storage scroll, preparing to seal the puppet away. This prototype was a failure, but it had taught him valuable lessons. The next iteration would need a different approach to generating physical energy. Something with far more cellular mass than a single heart.
He already had ideas forming.
He pressed the scroll against the puppet's surface and channeled chakra into the sealing formula. White smoke enveloped the failed prototype, and it vanished into storage.
"Just a matter of time. I'll figure out the right materials. Then I'll have my living puppet."