Koji started working on his dietary plan first. He came from a world where people could set up diets based on their exact weight and height, but here there was no tool to measure someone that precisely. Therefore, with relative estimates and understanding the sources of nutrition in the Ninja world, he could begin creating his own diet.
This part was simple, but the other 3 books were trickier. He was eager to start with Chakra, but when he read it, he could only grasp the concept of Chakra. In the Shinobi world, Chakra was a life force and a form of spiritual energy. He could figure this out just from watching the anime, so this didn't really help him. The problem he was having was actually sensing Chakra within his body.
The book explained how you should start by sensing the Chakra within your body, but Koji had no idea how to do that. He was happy to learn that meditating can help increase the connection with Chakra because that meant that the work he put in over the past 2 years was not wasted. However, even after meditating for an hour straight, he couldn't sense the Chakra in his body.
'Damn it!'
'This is hard, maybe it's because I am not from this world, but the idea of Chakra doesn't stick with me.'
After living in the modern era and never sensing anything similar to what Chakra is, it wasn't easy for Koji to suddenly sense this dormant energy.
'Whatever, can't help it, just gotta keep trying, I guess.'
He decided he would put a hold on his Chakra sensing for the day and started reading the other books. He decided to read the one about shuriken throwing later because he couldn't practice that in his room anyway.
As he read through the book on the basics of human anatomy, he felt that this was the only thing that could give him immediate results. The vital spots in the human body were something he could just memorize and eventually practice in a more technical setting. So he spent the rest of the day, slouched in his room, taking notes on the major organs and joints of the human body.
Eventually, Yuna called him for dinner, to which he suggested she start making food according to his newly formed diet. There wasn't any major difference to the food she was already making, so she agreed without much thought.
Two more years passed by as Koji eventually found himself walking through the Uchiha compound. One difference from the anime was the people in this clan, he noticed how the anime portrayed them as very violent and prideful. However, the non-shinobi families living in the compound were no different from those living in the village. They were humble and greeted all clan members and even non-clan members warmly.
"Koji, come here and have some fruits. Tell Yuna it's a gift from us."
He looked in the direction of the voice only to find an elderly woman with a smile on her face. Yuna would frequent her shop for groceries, and the woman and her husband had always been very kind.
"Thank you very much, Auntie Miyuki! I'll be sure to let mom know."
After taking the bag of fruits, Koji decided to head back home.
'The Second Great Shinobi War had begun earlier this year. Although I was off in the timing by a bit, it is still relatively similar to the plot I remember.'
When he returned, he left the bag in the kitchen and headed to his room again.
With the war, Koji felt even more pressure to get stronger.
'Luckily, the years were not wasted, my accuracy in shuriken throwing is pretty good right now. Although I can't precisely hit vital points, I can hit the general range of where I am aiming, and if I am lucky, then I might even hit a vital point.'
Koji had been trying to get his shuriken-throwing skills to be as accurate as possible over the years. His recognition of vital points in the human body meant that he had targets, but if he couldn't hit those targets, then it would be useless.
'Well, one thing is for certain after these two years of training... I am no genius.'
Koji knew that the rate at which he progressed in his shuriken throwing was by no means fast. But he still believed that due to his diligent practice, he had managed to get a grasp on throwing multiple shuriken at the same time, with all of them at least hitting the target. If he only used one, there was about a 95% chance that he could get a bullseye even if the target was moving.
However, this wasn't the only thing he worked on over these years. He had begun learning basic fighting stances and even learned the Uchiha clan's taijutsu style. He actually really liked the clan's fighting style as it relied on precision and reaction speed. This meant that he could engage and disengage from a fight instantly, just like a shinobi should.
'There is no reason a shinobi should be fighting drawn-out battles; it should be quick, not a brawl.'
"Anyway, now that I am 4 years old, and the war has begun, the Ninja academy has started admissions earlier for children."
Normally, children could enroll in the Ninja academy at around 6 years old, but because of wartime, when there is an increased shortage of ninjas on the front lines, the process of training these kids into shinobi becomes much shorter.
'I have just about a year left before I will have to join the Ninja academy, and if I show exceptional talent, or even some talent, they make me graduate early and send me to war. That's the worst thing that could happen, so although I need to prepare myself for the war, I need to do my best not to stand out in the beginning because that could end up bad.'
"Alright, time to get to work."
Koji left the house and went to a nearby training ground, this was where he normally went to practice shuriken. However, today was different. Today he was going to practice Jutsu!
'It took two years, but I finally started sensing my Chakra, I can feel the energy flowing within me, and I can even move it within my body. It didn't take long for me to learn the handsigns. The handsigns helped a lot with the movement of Chakra in my body. So now, it's time to learn my first Jutsu.'
It took quite some convincing to get this from Yuna, but Koji finally got his hands on the scroll for fireball jutsu, the signature jutsu of the Uchiha clan.