Sai was an orphan ever since childhood and was taken and trained by The Foundations. During that time he befriended an older Foundations member, Shin. They became really close and Sai began to look up to him as an older brother. Sai made a book depicting all the enemies they both faced and defeated to show the bond that they had. It showed Sai on one end of the book and Shin on the other end and the last page that was supposed to show Sai and Shin together was left blank due to Shin's death before they were supposed to fight each other to the death. After that, Sai was able to completely shun his emotions until he met Naruto when he was assigned to Team Kakashi as Sasuke's replacement by Danzo. Sai soon began to restore his emotions and was able to finish the book with a last picture of both of them holding hands with each other. Sai is now still part of Team Kakashi as Sasuke's replacement and continues to learn more about emotions.
Sai is a an awkward person who doesn't know how to behave. He enjoys reading books about learning how to behave like a normal person but ironically only makes him more awkward. Sai holds a special connection with bonds between brothers. This was shown when he tried to preserve Naruto's and Sasuke's bond.
Sai is known for his drawing abilities. He uses a special jutsu to bring these drawings to life. Usually these drawings are of animals.
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