Once he'd checked on his students' progress, Kenji turned his attention back to the Rasengan's third stage.
This was where things got brutal.
The first two stages had been challenging but straightforward. Stage one taught rotation, churning water inside a balloon until internal pressure exploded it. Stage two taught power, condensing chakra into a focused point to burst a solid rubber ball. Both had clear objectives and measurable results.
Stage three demanded both simultaneously.
He had to maintain the chaotic high-speed rotation from stage one while also compressing the chakra to a single point like in stage two. All while forming a stable membrane between the spinning chakra sphere and the balloon's inner surface. The balloon itself was only a few millimeters thick. One mistake in chakra control and it would burst instantly.
It required precision at a level he'd never attempted before.
His first attempt lasted maybe two seconds before the balloon popped. The chakra spiral destabilized, lost its shape, and tore through the membrane he'd been trying to maintain.
"Damn it."
He tried again. Three seconds this time before failure.
Again. Four seconds.
The problem was clear. His muscle memory hadn't internalized the previous stages well enough. He was still consciously thinking about rotation and compression as separate actions, which created microsecond delays when transitioning between them. Those tiny gaps in focus were enough to destabilize the entire structure.
He needed both operations to happen automatically, like breathing. Only then could he maintain the delicate balance required to keep that thin balloon intact while violent forces churned inside it.
After his fifteenth attempt, the balloon finally held for five full seconds before exploding.
He was starting to get a feel for it though. The rhythm of chakra flow, the timing of compression, the way rotation and power needed to merge into a single unified motion rather than two separate techniques.
Then he checked his chakra reserves.
Nearly half gone already.
The Rasengan was expensive to train. Pure shape manipulation with no elemental component meant dumping raw chakra into every attempt. Naruto could spam this training all day because his reserves were massive, boosted by the Nine-Tails. Kenji didn't have that luxury. He had to be careful.
The remaining half of his chakra was his emergency reserve. If something went wrong, like enemies showing up or an urgent mission coming down, he needed enough chakra to fight or escape. Burning it all on training would be stupid.
He walked over to a tree and sat down, pulling out a scroll on sealing techniques. Might as well study while his chakra regenerated. Multi-tasking was efficient.
He'd been reading for maybe ten minutes when a voice called out, breaking his concentration.
"Sensei! I did it!"
He looked up to see Aoi sprinting across the water's surface. Her clothes were soaked and water dripped from her hair, but she was grinning like she'd just won the lottery. She waved enthusiastically as she ran toward the shore.
"Knew it," Kenji muttered to himself. "Her control's always been exceptional."
Aoi reached the riverbank. "I really learned water walking! It works! I can actually do it!"
Water droplets flew everywhere as she moved, splattering on the grass and rocks.
"Good work. I figured you'd master it quickly." He stood up and placed his hand on top of her head. "Hold still for a second."
He channeled fire chakra through his palm, carefully controlling the temperature. The energy spread across her body in a thin layer, warm but not hot enough to burn. Within seconds, steam began rising from her clothes and hair as the moisture evaporated. The damp fabric dried somewhat, and the water clinging to individual strands of hair vanished.
Thirty seconds and she was completely dry.
Aoi's eyes went wide. "Whoa! How did you do that? That was so cool!"
"It's a controlled application of Fire Release principles. Fire chakra, at its core, is about transforming your chakra into heat, intensifying the vibrational speed of molecules to generate warmth or flames. Here, I'm not forming a full jutsu like the Great Fireball Technique; instead, I'm channeling a low-intensity flow of fire chakra directly from my tenketsu points, spreading it evenly across the surface. The heat accelerates evaporation by breaking the hydrogen bonds in the water molecules clinging to your skin, hair, and clothes, turning them into vapor without raising the temperature high enough to scorch fabric or cause burns. It's all about chakra control." He pulled his hand back, unable to completely hide his amusement at her reaction. "You can learn it once your chakra control improves."
He glanced toward the river where Haruto and Kaede had stopped their own training to stare at Aoi with envy. Their movements had slowed while they watched.
Time to motivate them.
"Hey!" Kenji raised his voice. "Look at Aoi, then look at yourselves! Have you been slacking off or what? Is this really your best effort?"
The boys flinched. Haruto immediately scrambled back into position, chakra flaring at his feet as he attempted the technique again. Kaede followed suit half a second later.
They both fell in immediately.
Splash. Splash.
Kenji shook his head as they surfaced and started over. They were trying, at least. Just not very successfully.
Still, he couldn't help comparing them to Aoi.
"Girls really are easier to teach," he muttered under his breath.
In his previous life, he'd worked with colleagues who had sons. They'd always complained about how much harder boys were to manage compared to daughters. He'd thought they were exaggerating. Now he understood completely.
Aoi absorbed lessons quickly, practiced diligently without needing constant supervision, and listened to instructions. Haruto and Kaede needed to be yelled at every thirty minutes or they'd start goofing off. The contrast was exhausting.
He settled back under the tree and returned to his scroll, occasionally glancing up to make sure his students hadn't drowned themselves.
The next day found them at the same river, continuing training.
Haruto and Kaede were still working on water walking. They'd improved slightly. Now they could maintain balance for three or four seconds before their chakra control slipped and they sank. Progress was progress, even if it was slow.
Aoi, having already mastered the exercise, had moved on to taijutsu drills. One of Kenji's shadow clones was working with her on the riverbank, demonstrating proper form and correcting her mistakes. The clone was way more patient than Kenji himself would've been. That was one advantage of shadow clones, they didn't get frustrated or tired of explaining the same thing repeatedly.
Originally, he had planned to send her to the field hospital for practical medical experience. Both of them had learned medical ninjutsu from scrolls, which meant they could handle basic battlefield treatment but lacked real experience. Medical-nin needed to see hundreds of different cases to truly develop their skills. Theory alone wasn't enough.
But when he'd inquired about it, the hospital administrator had shut him down immediately.
Konoha hadn't implemented the medical reform program yet. All hospital medical-nin were graduates of specialized medical training programs with strict certification requirements. Self-taught practitioners like Aoi, no matter how skilled, weren't allowed anywhere near patients. She couldn't even assist with basic tasks. The administrator had been polite but firm. No credentials meant no access.
Guess I'll have to figure something else out, Kenji thought, watching his clone adjust Aoi's stance during a punch.
Maybe once the war ended and Tsunade pushed through her medical reforms, opportunities would open up. Or maybe he could arrange a direct introduction to Tsunade and see if she would be willing to provide some guidance.
He didn't plan on becoming a medical-nin himself. His path was somewhat clear, puppetry combined with the Yamanaka mind techniques and whatever other skills he could pick up along the way. But having a skilled medic on his team would increase their survival odds. In a world where combat was constant and injuries were inevitable, a reliable medical-nin was worth their weight in gold.
That was why he had such high expectations for Aoi. If she could reach even half of Tsunade's level eventually, their team would have a massive advantage.
While Aoi trained with the clone, Kenji returned to his own practice.
The Rasengan's third stage was still giving him trouble, but he was making progress. Yesterday's training had helped him internalize the basic rhythm. Now he could keep the balloon intact for ten seconds consistently before it burst. The problem was fine-tuning. Occasionally his chakra output would fluctuate by a tiny amount, just enough to destabilize the rotation or compression, and the whole structure would collapse.
"I just need more repetitions," he told himself. "Muscle memory will handle the rest eventually."
The real limitation was his chakra capacity. He could only train for about thirty minutes before needing to stop and recover. Nowhere near as efficient as Naruto's training schedule would be. But there was no point complaining about genetics.
He formed the technique in his palm once more, feeling the chakra spin and compress simultaneously. The balloon trembled but held. Five seconds. Seven. Nine. Eleven.
Pop.
He tried again. This time the balloon lasted thirteen seconds before bursting.
Better.
By the time his chakra reserves dropped to the halfway point, he'd managed to maintain the technique for nearly twenty seconds. Still not complete mastery, but he was getting there. Another few days of practice and he'd have it down.
He stopped training and moved to a flat rock by the river, pulling a strip of dried venison from his pack. He chewed slowly, letting the salt and protein settle in his stomach, just simple calories to fuel the body's natural chakra regeneration. Eating while the reserves were low kick-started the recovery cycle: nutrients entered the bloodstream, his body absorbed the energy and converted it back into usable chakra.
Once the last bite was gone, he sat cross-legged on the rock, hands resting on his knees. The water flowing past provided a pleasant ambient noise that made meditation easier.
When his reserves had recovered sufficiently, he reached into his supply pouch and pulled out a storage scroll. This one was different from the standard equipment scrolls. It had two separate sealing formulas inscribed on it, each marked with a single word.
"Puppet" and "Heart."
He placed his hand on the "Puppet" seal and channeled a small amount of chakra to release it.
White smoke puffed outward. When it cleared, a small humanoid puppet about half a meter tall sat on the ground.
The construction was basic. Dark hardwood frame, minimal detail work with decorative elements. It looked mass-produced, like something churned out from an assembly line for quick deployment. Completely unremarkable.
He didn't care about aesthetics. This puppet had a specific purpose, and looking pretty wasn't part of the requirements. He moved his hand to the second seal, the one marked "Heart," and released it as well.
More smoke.
When it dispersed, a glass container filled with pale green preservative fluid appeared in his palm.
Suspended in the liquid, a heart beat with slow, steady rhythm. The same heart he'd harvested from the Iwa ninja's corpse.