Like the elemental jutsus of rank D, the Genjutsus in the public library were of a low level.
Aside from the theory of Genjutsus and how they affect your enemies, there were fewer than 10 Genjutsus that could be learned.
These Genjutsus were of a low level and only a civilian without chakra training could be affected, as they were very easy for a trained ninja to detect in their chakra pathway systems.
But even though they were low-level Genjutsu and there were very few of them, they were very useful to Natsuo because in addition to understanding how to deceive the mind, he learned Yin Release and read a little about Yang Release.
Apart from the 5 elemental natures: Fire, earth, water, wind and lightning and their bloodline limits when combining 2 or more natures, there were 2 more natures: Yin and Yang.
To put it simply, Yin release can give things form, and Yang release can give them life.
The Yin Element is an element based on spiritual energy that governs imagination; it is used to create forms from nothing. The Yang Element is an element based on physical energy that controls life.
The Yin element is used in Genjutsu and the Yang element in medical Jutsu.
Furthermore, clans like the Nara and Yamanaka use Yin Release, and the Akimichi clan used Yang Release in their secret jutsus.
Natsuo was interested in medical jutsu so he could heal during or after a battle, but he couldn't just ask to be taught at only four years old. They would think it was a joke.
That is why for now he will concentrate on Genjutsu and the applications of the Yin element in his own mind.
As an Uchiha, however diluted his blood may be, he will have more affinity for the Yin element than for the Yang element, so it would be optimal for him to start with it first.
After having read and memorized the theory of Genjutsu during the following week, Natsuo read and memorized the Genjutsus that he could learn before returning to the orphanage.
But before he could enter the orphanage and go to a secluded place to practice Genjutsu, he was interrupted by his little friends who pulled him to go play.
Sighing, Natsuo let himself be pulled along and accompanied them to play until the afternoon.
.
.
.
That same night, Natsuo practiced the hand seals of the Genjutsus he had learned in the clan's library.
These were low-level Genjutsus that would only affect a civilian without ninja training, so they were easy for Natsuo to perform, who had excellent chakra control.
The difficult part was constantly practicing these Genjutsus and understanding the purpose of each hand seal.
There was a Genjutsu that would make a civilian ignore the caster, a Genjutsu that would force the target to answer a question or perform an action, Genjutsus that deceived the target about what they see and feel, etc.
These Genjutsus were simple and easy. And although they wouldn't fool a ninja, they were useful to Natsuo and taught him the applications of Yin Release in the mind.
And although Natsuo had no one to practice these Genjutsus with, for now it wasn't necessary because he could practice on himself.
To use Yin release, one first had to transform their chakra into the Yin element.
And how was that done?
The Yin release user must first create Yin chakra using 2 parts spiritual energy and 1 part physical energy.
Luckily for Natsuo, the book also mentioned how to form Yang chakra, and it was very simple.
The Yang chakra is created similarly by using 2 parts physical energy and 1 part spiritual energy.
Once you have created Yin chakra, the user should study it and, knowing what it is like, try to transform the chakra in their body into Yin chakra.
Otherwise, it would be very annoying to have to constantly create Yin chakra to cast Genjutsus and other secret jutsus.
For Natsuo, it was very easy to remember the sensation that the Yin chakra gave him, and it only took him a few hours to transform some of his normal chakra into Yin chakra.
With the Yin chakra ready, Natsuo guided it through his chakra pathway system to his brain and attempted to change what his brain perceived through his eyes as instructed in the Genjutsu books.
As Natsuo desired, his perception of his surroundings told him that he was no longer in his room, but rather in the middle of the clan compound, walking towards the library when in reality he was lying cross-legged on his bed.
Natsuo also realized that the Genjutsu book he had just thrown said the correct thing about not being able to deceive a ninja because he felt that what he was seeing was fake.
His instinct sensed that something was wrong and he focused on his chakra pathway system where he found the Yin chakra influencing his brain.
If Natsuo, a novice, realized this, it was obvious that a trained ninja would not be fooled by this Genjutsu.
Higher level Genjutsu would be necessary if Natsuo wanted to deceive a genin, chunin, or jounin.
Let alone a Kage-level ninja. Only S-Rank Genjutsu could deceive a Kage-level ninja.
Natsuo was happy with his progress and continued to change his perception.
He could even deceive his sense of touch when greeting people he remembered seeing while walking around the clan.
The only things that could tell him he was being influenced by a Genjutsu, apart from feeling the influence on his chakra pathway system, were people's voices.
Having never spoken to these people before, Natsuo's brain had to create the new voices, and many of them were repetitive or sounded fake.
Satisfied with his progress, Natsuo lay down and quickly fell asleep.
What Natsuo wouldn't find out until much later was that other ninjas need months or years to accomplish what he did in a matter of minutes.
Having greater mental strength due to his rebirth and his imagination played a crucial role in his rapid progress.
.
.
.
The next day Natsuo added a new routine to his training.
In addition to lightly training his body while playing with the other children at the orphanage, he used his newfound abilities to accelerate his learning.
After returning from the library, he would lock himself in his room for a moment to use Yin chakra and manipulate his mind to remember what he read in the library.
By lying about being sleepy after studying in the library, Natsuo was able to escape from his friends who wanted to continue playing what they played in the morning.
While lying on his bed, Natsuo's mind was working at full capacity, analyzing and organizing the information he had in his head in a library locked in a castle.
By being able to manipulate his mind, Natsuo spent several days meditating to create a mind palace where he arranged all his memories.
From daily life, knowledge he gained in both worlds, to his knowledge of the plot which he keeps very safely under the bookcase.
And of course, there were countless false memories and useless information.
As a defense, there were many rodents, wolves, birds, and insects around the castle who patrolled the area looking for intrusions.
Having a mind palace, Natsuo's learning accelerated by leaps and bounds, and he continued his routine all year round.
In that way, almost 2 years passed quickly.
.
.
.
Year 29 of the creation of Konoha
Around the Uchiha clan territory, a group of children could be seen running at full speed.
These children were young members of the Uchiha clan, who ran around the clan grounds as part of their training.
All of them were children from the Uchiha clan who attended the village's shinobi academy, except for Natsuo who joined the group almost a year ago, days after turning 5.
After this year ends and another one begins, Natsuo will have to attend the academy.
Wanting to know what he would learn at the academy, he approached his older orphaned classmates and asked them.
Thanks to them, Natsuo learned about the physical training that a group of children from the Uchiha clan did in the mornings, and Natsuo joined shortly after.
Not only were orphans running here, but also the other children of the Uchiha clan who attended the academy.
After all, the Uchiha clan couldn't train all the clan's children with the best resources.
So they only trained the best and let the others attend the village academy.
After running for half an hour, Natsuo and a few others slowed down while the rest continued onward.
Those who continued moving forward were the older ones, while the younger ones slowed down to rest.