A few minutes later, Kakashi led his three disciples to the forest behind Tazuna's house for training. The Land of Waves was surrounded by mangroves that protected the land from erosion, but Kakashi had taken them farther inland, meaning they were in a regular forest.
So, no water surface walking training just yet, but that was putting the cart before the horse! First was the leaf-sticking, then tree-climbing, then finally water-walking!
"All right, let's begin!" Kakashi called out to them. "Let's start out with the basics: the energy we shinobi use every day, our chakra."
Naruto looked extremely lost; it was a good thing that he was naturally gifted, because he had very clearly never put in a hard day's training in his entire life. And no, doing push-ups in your bed didn't count.
"How can you not know what chakra is?" Sakura said as she gaped at him. "Chakra is literally your one and only redeeming point, and you don't even know what it is!?"
"Sakura, you explain it to him," Kakashi sighed, completely discouraged.
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'We've already gone over the difference between stamina-chakra and Jutsu-chakra in the Beautiful and Busty Kunoichi Sakura's Learning About Chakra Corner!' Inner Sakura shouted. 'Go read chapter 13 again if you've forgotten the difference!'
As a reminder, stamina-chakra is what courses through one's chakra pathway system (the blue stuff Neji sees when he uses the Byakugan) under ordinary circumstances. Through the process known as moulding or kneading chakra, spiritual energy, of which one has nearly limitless amounts of, is mixed with the physical energy (stamina) drawn from the body's trillions of cells via the chakra pathway network.
This kneading process occurs in the vital organs, and it produces chakra useable for Ninjutsu, Genjutsu and sensory-type Jutsu. Produce too much useable chakra and the extra goes to waste; too little, and your Jutsu fails!
At first glance, one might think that it doesn't make sense that base Naruto has so much chakra, since chakra is a 50/50 mix between physical energy (stamina) and spiritual energy (willpower and wisdom). He obviously has a lot of stamina because of his Uzumaki vitality, but isn't he a smooth brained idiot who doesn't even have enough brain cells to rub together? Why does he have so much chakra, one might ask!
The answer, of course, is precisely because Naruto has tons of stamina! Even though he wastes most of it by getting the 50/50 ratio wrong, he still has enough stamina to spare to easily make up for the difference. Since it's pretty much impossible to run out of spiritual energy (unless you get depressed or lose the will to fight), as long as Naruto has stamina, he has chakra.
(Also, spiritual energy does not equal smarts; otherwise Shikamaru would be a Kage-level threat if he trained his body even a little)
Finally, you die if you run out of chakra. Since stamina-chakra is intimately tied to the amount of energy in your cells, if you extract too much stamina from your cells to produce Jutsu chakra, there won't be enough left to support your cellular activity, meaning that your cells, organs and body will quite literally shut down; in that order.
'This concludes the Beautiful and Busty Kunoichi Sakura's Learning About Chakra Corner!' Inner Sakura declared. 'I hope you did more than just stare at my breasts while I was talking, Naruto, you pervy bastard!'
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A few minutes later, Sakura finished up explaining everything there was to know about chakra to Naruto, minus nature energy, Senjutsu and the true origin of chakra. She couldn't reveal what she wasn't supposed to know, after all.
"I still don't get it," said Naruto, shaking his head and crossing his arms in front of him. "I'm more of a physical learner, so I'll get it if you just show it to me, ya know."
"For once, Naruto's right," Sasuke pointed out. "We already know how to use Ninjutsu, so what's the point…"
"You know how to use Ninjutsu, but you're not using it as effectively as you could be!" Kakashi interrupted. "Your control is lacking. You need to learn how to perfectly balance the physical energy you extract from your cells with your spiritual energy; otherwise, you'll only be wasting your stamina."
"I'm still lost," Naruto said, rubbing the back of his head sheepishly. "So… er… how do we get better at using chakra?"
"Why, by climbing trees, of course," said Kakashi, as if it were obvious. "Ah, but for this exercise, you can't use your hands."
To prove his point, Kakashi shoved his hands in his pockets and began slowly walking up the side of a large tree. He then leisurely walked over to a branch, and by that point, he was completely upside-down.
"The point of this exercise," he explained, "is to train you to balance these energies effectively, and to use just the right amount of chakra for your purposes; no more, no less. Furthermore, since the soles of your feet is the area where it is most difficult to emit and manipulate your chakra from, this exercise will teach you how to perfectly control your chakra.
Tree-climbing really was the perfect all-in-one exercise. Multitasking chakra kneading and chakra control was something all shinobi had to master; after all, you wouldn't be able to call for a time-out in actual combat to knead more chakra! You've gotta do it all on the move, while dodging and while fighting!
"All right, enough talking; you'll never learn if I keep yapping on and on," Kakashi called out to them from the underside of his tree branch, before letting three kunai knives fall at their feet. "Here's some kunai; use them to score the bark at the highest point you're able to climb to— try to best that height each time you retry. Oh, and I'll be needing those kunai back, once you're done."
"Easy peasy!" Naruto called out. "Just watch me, Sakura-chan!"
Naruto took off running, but as soon as he put a foot on the tree he had picked, he slipped and fell over backwards. As for Sakura and Sasuke, they made the ram seal and closed their eyes, trying their best to summon their chakra and mobilize it to their feet.
Sakura ignored Sasuke, who had taken a running start and managed to run a good distance up a tree. It was useless for her to rush things, so she took her time to properly coat the bottom of her feet with chakra; if the original Sakura could do it on her first try, then so could she.
Sakura then tried taking a step forward, but she found that her foot was firmly stuck to the ground. That was a good start! And this was giving her an idea: couldn't this stickiness be used in melee combat to climb over foes, or to tear off their skin or equipment by sticking to them?
She wondered how it all worked; Van der Waals forces, perhaps? But what was chakra even made of, anyways? Atoms? Energy? It truly was a miraculous substance, capable of turning matter into energy, and energy into matter…
Sakura tentatively withdrew the chakra from the sole of her right foot and tried lifting her leg. It did not stick any more…