Yomi was a neighbor of Kaida. As Kaida's parents were out on missions most of the time, he usually stayed at Yomi's house. Needless to say, they became friends during that time.
When the Nine-Tails attacked the village, both of their parents died. However, before Kaida's parents died, they were able to save Kaida, Yomi, and many more civilians. Unfortunately, they were not able to save Yomi's parents.
When they were brought to the orphanage, Kaida became a supporting pillar for Yomi, who cried for many weeks after the incident. Kaida tried to stay strong for her and cried alone so that Yomi would not see him and remember those bad feelings.
Before his death due to that fight, Kaida always tried to make Yomi smile.
On the other hand, Yomi was devastated after her parents died, and the only person who remained with her was Kaida. That's why when he said that he would become a ninja, she became downhearted. Only when he said that she would also become a ninja with him did her heart stop aching.
He was the reason she continued the grueling training daily, so that she could always be with him and protect him from danger, as he was the last person she could call family. Slowly but continuously, this became an obsession for Yomi.
On the other hand, when Kaida first came into the body, he thought he had just inherited the body of the boy. But the reality was different—he not only received the memories but also the feelings and emotions of Kaida. So, it was more like Kaida received the memories of a 13-year-old boy from Earth, but since a person is just a collection of different memories, it would be more correct to say that somehow two people merged on that day.
So, he felt genuine care for Yomi and felt the same way for her as she felt for him, except for the obsession.
…
Since they had decided to focus on increasing their chakra reserves, Kaida and Yomi made three and one clones, respectively, and all six of them went to the library to learn about many things, such as the world and its geography, tactics to use in fights, and even biographies of various ninjas, mainly written by elite Jonins and above. Most importantly, they studied shogi.
Love this novel? Read it on Royal Road to ensure the author gets credit.
Each of them went to a different section and started reading. Each of Kaida's clones went to Yomi and explained the topic they read, and Yomi's clones did the same. They dispersed themselves before the information became too overwhelming and caused severe headaches from receiving memories.
At lunch, they just went out for a stroll as by then, all the clones had dispersed.
After eating a nutrient bar, they went back to the library and started absorbing knowledge again.
They repeated this for four days, and by the end of the fourth day, they had already read and understood most of the books in the civilian section. Now, they had a basic understanding of many things in the world. They also started playing shogi at night—one game with each other and another between their clones.
On the fourth day, when they were reading books in the E and D sections of the library, they discovered a book on the topic of spiritual energy.
When they read the book, they understood that what Hiruzen had told them was right: spiritual energy increases with an increase in knowledge and the thinking capacity of the mind. But at some point, it will stop increasing with just knowledge and will fully depend on experience. This means it will also increase gradually, like physical energy—through experiences of friendship, helping others, using others, or being betrayed. Everything counts and increases your spiritual energy.
Since they still had quite a large margin where they could increase their chakra by increasing knowledge, they decided to continue increasing their chakra/knowledge for the time being.
While they were learning in the library, another debate was taking place between some of the most powerful people in Konoha.
"The work in the shadows requires specialty and talent; I need those two so that our village will remain peaceful."
"Don't try to persuade me like with other orphans, Danzo. I know how most of them don't even have a say left in their own lives—you control them like puppets.
And using the same reason, you have already added many young talents to Root. Don't forget, one of them has Uchiha blood. I don't want the ire of a full clan just to satisfy someone's greed for talent."
"No one will know about their disappearance, so you don't have to worry about the Uchiha."
"I already said no—end of the topic. Just like the dark, some talented ninjas should also be present in the light of Konoha."
Danzo just stood up and left, as Hiruzen was dead set on not giving him those two new bloods.
One of the reasons Hiruzen decided to keep them from Danzo was because it was Kaida's father's dying wish that Kaida should become one of the most respected shinobi of Konoha.