Konoha Village
Since returning from the front lines, Ren Kurogane and his team had settled into a new rhythm of life.
Nawaki made it his daily mission to pester Ren. In response, Ren ordered him to run ten laps around the village every single day. Initially, Nawaki protested with every fiber of his being, but after being "educated" by Ren a couple of times, he became a model student, dutifully completing his laps.
"Right, right! Put it down gently! Easy does it!"
"Hey! You on that side..."
Ren was currently directing a team of shinobi who were delivering equipment, urging them to handle his "treasures" with the utmost care. The shinobi remained expressionless; they were just there to do a job. As long as the pay was good, they were happy to accommodate any request, no matter how eccentric.
Once the lab was finally empty, Ren looked at the collection of cross-era machinery, and the corners of his mouth curled into a predatory, ambitious smile.
"Next up is blood research. Now, who should I start with?"
Just as Ren was contemplating his options, the boisterous voice of a certain blockhead echoed from outside.
"Master! I'm here for training!"
Hearing Nawaki's voice, the answer to Ren's dilemma presented itself instantly.
Snap!Thud!
The door flew open. Ren grabbed Nawaki, hauled him inside, and slammed the door shut.
He tossed Nawaki into a corner and produced a large syringe, a gentle, almost grandfatherly smile on his face. "Be a good boy now. Don't move, and it'll all be over soon!"
"No... NO! STAY AWAY FROM ME!!!"
A few minutes later, Nawaki sat slumped on the floor, tears pricking his eyes, looking very much like a victim of a grave injustice.
"Alright, go run your laps around the village. When you're done, find Minato to work on the Rasengan. Don't bother me unless it's an emergency." Ren waved him off dismissively and returned to his equipment, eager to begin analyzing the Senju lineage.
While he planned to hand the data over to Scientist Ren, the researcher in him wanted to take a look first. It would be a waste of the knowledge he'd inherited not to try.
Nawaki left Ren's grand villa, feeling utterly dejected. The puncture wound on his arm had already healed. He let out a long sigh and began his training for the day.
While running his laps, he ran into his "big brother" figure, Might Duy. The two began to race, pushing their speed until they both eventually collapsed onto the ground, gasping for air.
Might Duy was the father of Might Guy, but compared to the future Guy, Duy's generation was far more difficult. Training martial arts without wealth meant burning through one's life force and overdrawing on the future. As someone not from a "Secret Art" clan, Duy felt that risking his life was the only path forward.
Fortunately, he had met Nawaki. Whenever they finished a session, Nawaki would share high-quality body-tempering resources with him. Over time, Duy felt his physical condition improving significantly.
Declining Duy's invitation for an extra set of exercises, Nawaki cheerfully headed off to find Minato.
After all, why focus on Taijutsu when Ninjutsu was so much more practical? Especially since he had massive chakra reserves; he'd have to be crazy to focus on punching when he could be throwing Rasenshurikens from a distance! The moment he saw that move on the battlefield, a voice in his head told him he had to master it.
Even after the Third Hokage classified it as a Forbidden Jutsu, Nawaki's resolve didn't waver. If his body wasn't strong enough to handle it? He'd learn Senjutsu to boost his durability. As long as he could learn the Rasenshuriken, Nawaki was willing to study anything.
He arrived at Lady Mito's residence to find Minato currently deep in the study of the Four Symbols Seal. Nawaki excitedly demanded that Minato continue teaching him the Rasengan.
Minato looked at him helplessly, handed him a balloon, and told him to get to work.
"I've already told you the method. You can practice on your own; you don't really need to come find me every day."
Nawaki looked a bit sheepish at that. It wasn't that he wanted to cling to Minato, but it had been three or four days and he still couldn't pop the water balloon. His "patience" was reaching its limit. He desperately needed to know the secret to breaking the damn thing.
"Minato! Just tell me the trick! I really need this!" Nawaki clasped his hands together in a prayer-like gesture.
"Well..." Minato looked conflicted. To him, popping the balloon wasn't hard at all; he had figured out the trick almost immediately. He had only been delayed by his own limited chakra reserves at the time. Why was it proving so difficult for Nawaki?
"Minato-sama!" Nawaki looked at him with puppy-dog eyes, making it impossible for Minato to refuse.
"Fine," Minato smiled. "Start your training. I'll watch and see where the problem is."
Overjoyed, Nawaki quickly filled a balloon with water and began.
Swish-swish-swish—!
The water balloon in Nawaki's hand instantly flattened into something resembling a spinning pancake, rotating at high speeds.
Minato was floored by the sight. Wait, this chakra density... He felt a pang of envy. His reserves were respectable, but compared to Nawaki, they were nothing. If Minato's chakra was a 1, Nawaki's was a 30.
Come to think of it, Ren's chakra reserves are terrifying too.
"RRRAAAAGH!" Nawaki stared intensely at the 'pancake' in his hand, pouring every ounce of focus into spinning the chakra, trying to force it to explode.
However, his method was fundamentally flawed. No matter how much power he poured in, he wouldn't get the desired result.
Seeing this, Minato sighed. "Sorry, Nawaki. I can't help you with that."
"Huh? Why not?"
Nawaki was so startled by the sudden comment that his control wavered. The chakra in his palm became chaotic and turbulent.
The next second, the balloon in his hand violently detonated!
BOOM!
The high-pressure spray of water hit both of them with enough force to actually sting. Minato winced. Seriously, just how much chakra does this kid have?
Nawaki himself was stunned for a moment, but then he erupted into a jubilant cheer!
"YES! I finally did it!!" He turned to Minato, eyes shining with hope. "Minato! I did it! Can we move on to the next stage of training now?"
Wiping the water from his face, Minato calmly produced another balloon, filled it with water, and handed it back to Nawaki. "Do it one more time."
The explosion just now had been a total fluke—a "blind cat finding a dead mouse" scenario. Nawaki had simply over-pressurized the balloon until it failed. He hadn't actually grasped the core principle of the Rasengan yet. Unless he could replicate the feat, Minato wasn't going to let him move on.