I paused in the middle of the next push-up so that I could talk without interruption. "The only major difference between the two is that the Rasengan is used for offensive purposes while the Kaiten is used primarily for defence.
Well, that, and the Kaiten requires the entire body to spin to help create the rotation while the Rasengan is done purely through chakra manipulation. Once I realized that it was easy to reverse engineer the Rasengan and figure out how the technique worked."
...
Kakashi scratched his chin thoughtfully as he went over what I just told him. And while I was lying through my teeth about how I learned the Rasengan, everything else I said was true. It was legitimately possible to discover the secret of the Rasengan through the Kaiten.
I was pretty sure that the only reason no other Hyuuga ever bothered to try and learn it before is because there was no point, there were plenty of other Gentle Fist techniques that were just as useful and far easier to master than the Rasengan. Even I only went through the effort of learning it for Naruto's sake.
"Hmm, that's certainly possible I supposed." Kakashi mused, sounding unconvinced. "Still, having a theory and actually learning it are two different things. The Rasengan is a difficult jutsu to use and it isn't so simple that you can learn it just by having a rough idea of how it works."
That was entirely true. Hell, Kakashi was understating it if anything. There was a very good reason why I avoided using the Rasengan whenever possible, preferring the Chidori or the strikes from the Gentle Fist over it. It was simply too hard to use.
A person's chakra capabilities were measured in three primary methods.
The first was chakra supply; simply put it was the total amount of raw chakra you had in your body.
The second was chakra capacity, which was the amount of chakra you could release in any given moment. This determined the rank of jutsu you could use. To use a high-level technique, like an A-rank jutsu, you needed to have a high chakra capacity. If you didn't then it didn't matter how much chakra you had. If you couldn't pour enough chakra into a technique fast enough then most of the higher end jutsu were beyond you.
Then there was chakra density. Chakra density affected the size and intensity of a jutsu. The denser your chakra was, the more potent its effect. Denser chakra would cause a fire technique to burn more fiercely, or a wind jutsu to blow more violently. Using the Katon: Great Fireball jutsu as an example, the larger your density the larger and hotter the fireball.
With very few exceptions, chakra density didn't vary much from person to person. It was almost universally the same no matter who you were. Which was completely fine as you didn't need to be born with naturally dense chakra to have it, that's where chakra molding came in.
Before casting a jutsu, you can gather and fold chakra onto itself while it's still inside you before releasing it, thus 'thickening' it. Most Chuunin only needed a fraction of a second to double or even triple the density of their chakra, so, for the most part, a person's natural chakra density didn't matter.
However, when it came to the Rasengan your chakra density made all the difference.
At its core, the Rasengan was nothing more than pure chakra condensed into a revolving sphere that was spun in place at a high speed. And while it was the rotation speed that allowed the Rasengan to 'grind', it was the chakra density that hardened it enough to make it work.
Think about it this way if the Rasengan was less dense then, let's say an average human's bone, then even if you tried to slam it into an enemy's chest then the Rasengan would be the one that shattered instead of the enemy's rib.
That was the real reason why the Rasengan was so hard to learn, the sheer amount of chakra density it needed was massive. When I tried to cast the technique, I needed to fold my chakra a dozen times over to make it work, which was a ludicrous amount. Even the Chidori only needed me to fold my chakra twice.
Ironically the very same reason that made it so hard to use was what made Naruto so good at it.
Naruto's chakra was dense, ridiculously so. While most people needed to thicken their chakra to make a jutsu work, Naruto had to do the opposite. She needed to 'thin' it out or else her chakra would simply overpower any jutsu under B-Rank that she tried to use. And while this might have been a hindrance for most jutsu, when it came to the Rasengan it was perfect.
Naruto's chakra was already so dense that she didn't need to thicken it. All she had to do was release her chakra and rotate it into a sphere. In the end, all she needed was a few short weeks of practice and she could create a fully formed Rasengan into her hand in the blink of an eye.
Which was impressive as hell.
The Rasengan might have been the only jutsu Naruto had ever managed to learn faster than me, and if it wasn't, then it certainly was the one with the largest margin. It took me almost an entire year to learn the bloody thing while Naruto, just like she had in the Manga, managed to get it down after a month.
No wonder Jiraiya had been so impressed. Learning the Rasengan that fast couldn't be explained away by pure talent, it was an achievement that bordered on the supernatural.
It was almost unfair how ridiculously strong her chakra network was, even at twelve years old I didn't think that there was anyone out there that could come close to rivalling her. And she still wasn't done growing.
Embarrassing enough, during training I had to resort to using the two-handed style of Rasengan that the original Naruto had to use in the show. It was the only way I could finally learn the damn thing. I swear Naruto laughed so hard at seeing me use 'training-wheels' as she put it that she almost hyperventilated. Even now, she could mold a fully formed Rasengan in less than a fraction of the time I did. Her chakra density gave her that much of an advantage.
It was only after I had tried learning the Rasengan that I began to get an inkling about just how talented the Fourth must have been. For him to fold so much chakra so fast, his chakra control had to be phenomenal. Not to mention his chakra supply. The technique was a chakra sink. Due to its density, the Rasengan ended up draining more chakra than any other jutsu I knew, even the Chidori didn't compare.
I had always wondered why Kakashi never bothered with the Rasengan but now I knew, it was simply too hard to use. I could cast a Chidori far faster than the Rasengan and at a fraction of the chakra cost to boot. Even if you factored in the screeching noise that gave the Chidori its name, it was still more useful to me than the Rasengan was. Especially now that, thanks to Kakashi's guidance, I was getting even faster at forming the Chidori with every passing week.
"I used balloons." I finally told Kakashi.
"Balloons?" He asked, arching an eyebrow in obvious bewilderment.
"Yes, balloons," I confirmed. "That's how I trained myself to mold the Rasengan. I first started practising on water balloons, trying to pop them while using only pure chakra. That helped me learn how to rotate my chakra. When I figured out how to do that and still hadn't been able to form a Rasengan, I decided to up the difficulty and switched to rubber balls. That taught me how to make my chakra denser.
Once I was finished with that I was technically able to mold a Rasengan but it wasn't any good. It kept falling apart whenever I tried using it on something solid. Didn't take long for me to realise that I needed to get better at keeping its shape together.
So for the next step, I decided to combine both lessons and used a normal balloon but this time, instead of trying to pop it, my goal was to form a Rasengan inside the balloon without bursting it.
This taught me how to properly hold its shape. Once I had completed all three of those steps, presto, I had finally been able to form a Rasengan. After that, it was rather easy teaching Naruto. Too easy actually, she ended up learning it far faster than I did."
Kakashi was giving me the oddest look, something that was a cross between amazement and suspicion, as if he couldn't believe what I was saying yet couldn't think of an alternative but to believe me. "…And you came up with this training method all on your own."
"No, I learned the technique from a comic book about ninjas. Of course, I thought up the idea myself." I snarked back and, unlike Naruto, I knew my blank white eyes wouldn't give me away. There was a reason why we Hyuugas were so damn good in poker. "Why? Where else would I learn it?"
"Nowhere, I was just … surprised by how similar it was to another training method someone else thought of," Kakashi admitted slowly before easing off, pulling his face away from mine as he returned back to his seated position on my back.
Which was when I realised just how tired I was.
I bit back a groan of agony as I pushed through another pushup, not having realised how hard I had been pushing my body while I was distracted by Kakashi's interrogation. But now that it was over it was hitting me like a sledgehammer.
"Which reminds me," I began, trying to sound casual and doing a good job of keeping my exhaustion from my voice. If there was one thing I learned about Kakashi was that, like his dogs, he could smell weakness a mile away. And there was no way I was going to give him the satisfaction of seeing how much his training was getting to me.
However the simple truth of the matter was that while the spirit was willing, the body was weak, and my body had long since reached its limit. Even as I finished another rep I could feel my arms trembling so badly that I knew they were about to give out on me any second. "How much longer do I have to keep doing these pushups?"
"Hmm?" Kakashi glanced down at me then blinked as if he was surprised to still find me there. "Oh, you're still doing that? You were finished almost five minutes ago." I felt a hand pat my head as if I were a dog, "Though it is nice to see you so eager to complete my training."
"Oh you are such a dic-" The rest of my words were cut off as my arms chose that moment to give up the chase, and I collapsed onto the ground, knocking the breath out of me.
Even before I hit the ground Kakashi was off my back and sitting on the ground next to me, legs crossed and already back to reading his book. "And this is why you need to work on your upper body strength duckling. If it was Gai's student, he would have finished a hundred more reps then you."
"Lee would have finished a thousand reps more, then started working on a thousand back-flips, followed by a thousand more squats before asking for even more by the time he was done. Which is exactly why Lee is a masochist."
I let out a groan as I flipped onto my back, enjoying the cool breeze as it swept over my body. "And I'd much rather be a sadist thank you very much. Kind of like you, now that I think of it."
Kakashi nodded sagely, eyes never leaving the book, "Yes, it always pays to be more like me."
...
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