The water balloon sat in Kakashi's palm like a trophy he hadn't earned. His hands were still trembling. He was still processing that when Renjiro spoke.
"The balloon was just the beginning."
Kakashi's grip tightened involuntarily around the intact sphere. He opened his mouth to respond—something dry, something defensive, something that would mask the dread coiling in his chest—but Renjiro was already moving.
His hand disappeared into a pouch at his hip, emerging with a small, folded square of paper. A storage seal. Kakashi recognised the type—compact, efficient, the kind used by shinobi who needed to carry more than their pouches could hold. Renjiro pressed his thumb to the seal's centre, channelling a brief pulse of chakra.
"Puff."
Smoke coiled upward, dissipating quickly to reveal a large sealed case. It was unfamiliar—heavy, dark, constructed of materials Kakashi couldn't identify at a glance. The case was covered in seals, its surface a lattice of kanji and spirals that seemed to shift when he tried to focus on them.
Curiosity warred with caution. Kakashi's eye narrowed, tracking Renjiro's movements as the older man unlatched the case and lifted the lid.
Inside, nestled in fitted compartments, lay a board.
It was not a training tool Kakashi had ever seen. The surface was smooth, dark, inscribed with channels and pathways that branched and converged like a river delta rendered in miniature. Seals marked every junction, every node, every turning point. The complexity was immediate, almost overwhelming—a web of connections that seemed designed to baffle the eye and challenge the mind.
Renjiro lifted it with the care of a craftsman displaying a masterwork.
"My invention," he said, and there was something in his voice—not pride, exactly, but satisfaction. The quiet confidence of someone who had solved a problem that others hadn't known existed.
He glanced at Kakashi, and a slight edge entered his tone.
"There's more to life than inventing jutsu, Kakashi. Many can create techniques." He turned the board slightly, letting the light catch on the inscribed channels. "Not many can create this."
Kakashi's eye twitched. The barb was not subtle.
'He's still not over that,' he thought. The apology he had given—the surrender—had not erased the wound.
'Fair,' he admitted silently. 'I earned that.'
Renjiro's thoughts flickered inward, brief and private. The board in his hands was the product of years of experimentation, of ideas pulled from memories of his first life—concepts like circuits, logic boards, pinball machines that bounced energy along predetermined paths. He had adapted them, translated them into the language of seals and chakra, and created something that had no parallel in the shinobi world.
He did not explain this. Some things were better left unspoken.
"Watch," he said.
He placed the board on the ground between them, settling it on the packed earth. Then he raised a hand, fingers positioned above one of the input seals at the board's edge.
A pulse of chakra was injected into the seal.
Light flared along the channels. The pathways glowed, tracing the board's geometry in lines of soft blue. Kakashi watched the energy move, his analytical mind engaging despite himself. The pulse travelled cleanly, following the inscribed channels without deviation, without loss. It reached a junction and redirected—splitting, merging, and flowing toward another node.
Renjiro's voice was calm, instructional.
"Speed, stability, brightness. These are the variables. You inject a pulse—not continuous flow, just a pulse. The seals guide it, contain it, prevent dissipation." He pointed to a junction where the light had bent smoothly around a corner.
"The board's logic determines the path. Angle, strength, timing—all of it matters. One mistake, one miscalculation, and the pulse destabilises."
He let the demonstration run its course, the light tracing a final arc before fading into the terminal seal at the board's far edge.
Kakashi's eye followed the last flicker of chakra. His mind was already working, dissecting the mechanics, projecting his own capabilities onto the task.
'This isn't just control,' he realised. 'This is calculation. Precision. Timing.'
He looked at the board's surface—at the dozens of pathways, the countless junctions, the seals that would require perfect synchronisation to navigate. The water balloon had been a test of basic rotation. This was something else entirely.
Renjiro continued, "The control nodes are timing-based. You must inject chakra at the exact moment the pulse reaches a specific junction. Too early or too late, and the path breaks. Failure conditions vary—some nodes cause the pulse to scatter. Others will trigger a drain that pulls chakra from you directly."
He let that sink in.
"The stability system tracks pulse behaviour. Stable movement is clean, smooth, consistent. Instability manifests as flickering, wavering, erratic brightness. The more unstable the pulse, the more likely it is to fail at the next node."
Kakashi's gaze traced the pathways, counting the junctions, estimating the required precision. The complexity was staggering. A single clean run would require dozens of perfectly timed injections, each one calibrated to the exact state of the moving pulse.
"Energy decay is built into the system," Renjiro said. "Chakra dissipates over time, loses strength as it travels. Amplify seals can boost it; drain seals can reduce it. Loop seals can send the pulse back through a section multiple times, increasing the difficulty with each pass."
He paused, letting the information settle.
"And then there's multi-pulse injection."
Kakashi's eye narrowed.
"One pulse is the baseline. You can also split a single pulse into multiple weaker ones, each following a different path. Tracking multiple pulses simultaneously, managing their collisions, ensuring they don't destabilise each other—that's where the real training begins."
He gestured to the board's surface.
"Pulses interact. They can absorb each other, combine into stronger flows. They can destabilise each other, scatter into useless fragments. Or they can collide and redirect, bouncing off each other's energy."*
He met Kakashi's gaze.
"The glow tells you everything. Brightness indicates strength. Flicker indicates instability. Fading indicates energy decay. You will learn to read the board like a second sense, to know exactly where each pulse is, what state it's in, what it needs to survive the next node."
Kakashi stared at the board, and for a long moment, he could not speak.
The water balloon had been simple. The genjutsu had been punishing, but straightforward—fail, suffer, try again. This was different. This was not a test of endurance or a lesson in fear. This was a problem that demanded a solution, a puzzle that required every fragment of his concentration, his precision, his patience.
'This is worse than the genjutsu,' he realised. 'The genjutsu ended. This… this will keep going until I get it right. And every failure has a cost.'
He thought about the Sharingan, about the drain he had lived with for years, about the way his body had never fully adapted to the eye that wasn't his. Renjiro had said he needed to rebuild from scratch. This board was the blueprint.
Respect—grudging, reluctant, but undeniable—began to form in his chest.
Renjiro watched the shift in Kakashi's expression. The resistance was fading, replaced by something more useful. Focus. Calculation. The recognition that this was not a punishment but a necessary path.
"Mastering this board," he said, "is the training goal. Not the balloon. Not the genjutsu. This." He tapped the board's surface. "When you can run a full sequence—multi-pulse, collisions, loops—without failure, you will have rebuilt the foundation you lost."
He let the words hang.
"And when you fail—"
Kakashi tensed.
"—the board will drain your chakra. Directly. Mimicking the strain of the Sharingan, forcing your body to learn efficiency under pressure."
He paused.
"No genjutsu this time. The board is your teacher. The consequences are physical, not psychological."
'The genjutsu had been effective, but excessive. He could have continued that method, could have carved the lessons into Kakashi's psyche through repeated trauma. But there was no need to waste eyes.' Renjiro thought. The Mangekyō had a cost, and every activation was a currency spent. He would use it when necessary, but not when a better tool existed.
He reached for the board, preparing to lift it, to hand it to Kakashi, to begin the next phase of training.
Then a voice shattered the silence.
"KAKASHI! THERE YOU ARE!"
The shout was loud, exuberant, completely at odds with the heavy atmosphere of the training ground. Both shinobi turned.
A young genin stood at the edge of the clearing, his green jumpsuit a violent splash of colour against the grey dirt and scorched earth. His hands were on his hips, his posture heroic, his smile so wide it seemed to generate its own light.
"I've been searching the entire training grounds for you!" He bounded forward, his movements a cascade of youthful energy.
"You disappeared without a word—this is not youthful behaviour, Kakashi! A rival does not simply vanish!"
Kakashi sighed. The sound was long, deep, and carried the weight of a man who had just realised that the ordeal he had been dreading was about to become exponentially more complicated.
'This just got worse,' he thought.
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