Today, Sasuke's new training spot was discovered by Rock Lee and two Jonin. Sasuke had noticed them watching him for several minutes, but he didn't react and kept his training.

After about half an hour, the silver-haired Jonin approached him and introduced himself as his new sensei.

"So, this is the Copy Ninja, Hatake Kakashi... They want to use the Sharingan to control me. It's really ironic," Sasuke thought.

Kakashi was apparently impressed with his training and asked him for a spar.

Sasuke had read the bingo book and knew that his new sensei was an A-rank ninja.

"This will be interesting. I wonder what my level is right now," Sasuke thought.

--- Sasuke's Flashback ---

Sasuke's original plan was for Neji to graduate and give him techniques from the library. However, his plan was seen through and disrupted.

As soon as Neji graduated, he was approached by his clan's head, Hiashi Hyuga. He ordered him through the seal that he was not allowed to share any technique with Uchiha Sasuke. It was obvious to Sasuke that Hiruzen and Shikaku were behind this.

His alternative plan was for Neji to master jutsu and then fight Sasuke with them. Sasuke could then copy the techniques with his Sharingan and avoid overstepping Neji's orders. However, Neji's affinity was earth, and Sasuke's was lightning. It was difficult for Neji to master lightning and fire techniques, and it wasn't worth the effort just for the D-rank in the library's genin section. The only useful technique that Sasuke managed to copy was the 'Earth Release: Double Suicide Decapitation Technique.' It was a very useful technique, but Sasuke's earth affinity was low, and without further training, he couldn't optimize the technique.

Sasuke wanted to master all the elements. He already knew that it was possible. After all, that's why Hiruzen was known as the professor. He wanted to use his strongest asset, the Sharingan, at its full potential, and he knew that mastering the elements was a must to be able to effectively use every copied technique.

His first step was to use his cheats. He called Neji to watch him perform the Fireball Jutsu. Sasuke knew the flow of the technique, but he wanted to learn what happens in the chakra points.

According to Neji, his chakra was filtered in his lungs' chakra points and it changed to fire.

After several questions towards Neji, Sasuke managed to conclude that the total amount of chakra did not change. What Neji called a filter was not actually a filter. The chakra points in his lungs somehow had the ability to transform all the elemental energies in his chakra to fire without any loss in chakra. At least, that was the initial theory.

However, according to the principle of conservation of energy, this was not possible. If chakra is energy and it transforms its form, there should be a loss.

"My knowledge of chakra is extremely limited, and maybe the loss is so little that the Byakugan can't detect it. I cannot be sure.

Considering how chakra paper works, everyone's chakra contains the main affinity in a greater degree than the other elements, and the amount is significant enough to affect the paper.

That means that chakra itself is a type of energy which contains the five elements in a strange balance. This balance is different from person to person.  The chakra points seem to work like circuits which perform operations with this energy."

After discovering Naruto's instinctual use of fuinjutsu, Sasuke was extremely interested, and he had developed a theory following his understanding of the elements and the nature of chakra.

"The Uzumaki were famous for their vitality and their huge amount of chakra. Maybe they are so in tune with their bodies that they can instinctively understand how chakra naturally behaves in chakra points. Maybe fuinjutsu is a language designed to mimic the chakra points and work like a circuit.

However, to prove this theory is a long and difficult process. If my theory is right, then fuinjutsu was never completely explored. The greatest grandmasters of fuinjutsu were members of the Uzumaki clan, and the most probable scenario is that most of the current grandmasters followed their teachings. However, if the Uzumaki only followed their instincts which are connected and restricted to human biology, that means that the art has never reached its true potential.

If I am right, fuinjutsu is a language with the ability to control chakra, which in turn is a higher-level energy that defines reality. And I still have not a clue about ying and yang."

Sasuke had only two scrolls as a reference, and each of them had hundreds of kanji, lines, and shapes on them. To reverse-engineer them blindly by playing with each character was like going blind into a war. Theoretically, it could be done, but it would require a huge number of resources. If he had a proper lab with advanced AI systems, he could pull it off. However, he didn't have a lab, he was being watched, and he didn't have time to lose. So, Sasuke decided to focus on his advantage, which was his 'rival'.

After forming his plan, Sasuke focused on replicating the transformation of chakra from its original form to an element. He decided to follow the example of chakra control exercises and start with a leaf.

" My chakra can create wrinkles on the paper because of my lightning affinity. Chakra paper is especially sensitive to chakra. The next step should be to focus and isolate the lighting and create wrinkles to a more resistant object like a leaf.

I can do the same with my fire element. Actually, it’s better if I start with fire because I can use the fireball jutsu as a reference. What I need to do it make the leaf ignite. 

I have to use the chakra point in my hands to make the transformation. My Sharingan copy technique is like a one-trick pony. Even though I can view the chakra movement, it doesn't help me much if I want to completely alter a technique. Also, I find Neji's descriptions lacking. My only options are hard work and clone abuse..."

In a few months, Sasuke managed to successfully produce fire and lightning from his hands with great success, and he was ready for the next step of his plan. Even though lightning was his main affinity, he had been training with fire since his youth and was really adapted to it.

"Maybe Uchihas are so fixated on the Fireball Jutsu because it is used as an entry point to elemental training and shape manipulation. The summary of this technique is converting the chakra to fire, using the wind that you have inhaled to propel it, and, in the end, giving it shape. It is like a perfect chakra control exercise."

His training with the other elements was not as successful. His chakra was resisting the change towards earth and especially towards wind and water. However, it was a matter of hard work and effort, and Sasuke made sure to have one clone focus on each element.

Neji was essential for the next part of his plan. Sasuke would perform the chakra transformation by turning chakra into fire using only one chakra point in his hand. Neji's job was to watch all the progress and draw several diagrams of the procedure.

It took Sasuke and Neji several days to completely copy the procedure on paper. The chakra point was altering and processing the chakra several times every second with peculiar ways. In the end, Neji's designs were a complete mess. He was supposed to create a flip book, but the result was a mess with lines, circles, and strange patterns. Both Sasuke and Neji flipped the book in a try to make sense of it with no success.

It was time for Sakura's second mission. Sasuke was excited and hopeful about the results, but surprisingly Sakura failed. Naruto told her that he didn't want to help her since she didn't appreciate his help.

Sasuke was extremely displeased with the girl. However, the most he could do was to express his unhappiness and refuse her the reward. After all, the girl was really good at medical ninjutsu, and she was helping him accelerate his physical training. Also, he still needed her to restore his clan.

His next option was Ino, who also got refused. Naruto told her that he didn't appreciate being taken advantage of and told her to tell her friend Sakura that he was not a fool.

Sasuke was displeased that his plan didn't proceed, but he couldn't really blame Naruto for this. The two girls disliked him, and they never really tried to hide it, especially Sakura.

After Hiruzen's warning against him, Sasuke didn't want to take the risk and approach Naruto. So, his only option was to wait.

Finally, in the last year of the academy, Naruto transferred into his class. After publicly proclaiming him his rival and after some small talks, Sasuke managed to close the gap between them. Unfortunately, Naruto was no longer the same boy. He now had friends, a Jonin teacher, and he was no longer hated. Sasuke wasn't sure if he could completely control him anymore. However, he still had some cards to play.

After two weeks in the same class, Sasuke felt comfortable to ask him for a favor. He gave him the flipbook and asked him to explain to him what it does.

Naruto spent the whole day flipping it and stopping at specific pages. At the end of the academy, he finally said.

"Sasuke, I am not really sure, but I think that this somehow describes chakra that burns, but the process is very strange... I tried to understand it, but it feels like something that happens without thinking, like moving your hands... I don't know, but if I spend more hours on it, I may be able to get it," Naruto said with a little frustration.

Sasuke was excited, and a huge smile appeared on his face.

"Naruto, thank you very much for your help. If you compare these pictures with the previous scroll that Sakura asked you about, how do you feel?"

Naruto was thoughtful for almost a minute.

"I feel like the previous scroll was concentrated and had less useless information. It was less confusing and it was more logical. This book feels like repeating the same things with different words and patterns again and again."

"This is it! So, what Neji sees with his eyes is like hieroglyphics compared to a modern structured language like fuinjutsu," Sasuke thought and said with a huge smile, "Naruto, I truly thank you for your time. If you need anything, don't hesitate to ask me!"

"Sasuke, we are rivals but also friends. There is no need to thank me," Naruto said.

However, from his expression, it was obvious that he was quite pleased with the compliment.

"After Sakura and Ino, I can't afford to be rude to the boy. I need to play my cards right and fully control him. He is way too precious for my research."