Sai is a character that doesn’t join the cast of Naruto until Part Two, after several hundred episodes of getting to know the rest of the characters in Naruto’s cohort. He replaces Sasuke in Team Kakashi after Sasuke leaves the Hidden Leaf Village and once Naruto returns to the village from training with Jiraiya for three years.
His backstory and the way that he interacts with Sakura, Naruto, and Kakashi make him a special addition to the team and a different experience for the characters than Sasuke, forcing them to learn how to interact with and work with a much different kind of ninja.
10 Training With Root
Sai grew up in training with Root, which was a very specific subsect of the Anbu, a ninja team that specializes in bringing in rogue ninja, usually by killing them. Root in particular trained its ninjas to not feel any emotions and to take orders without question. This allowed them to do missions that were unethical or difficult without feeling the pressure. Root was disbanded after its founder, possibly the least likable character in the series, Danzo Shimura died, and Sai and the other ninjas in the group were reassigned.
9 Relationship With Kakashi
Like Sai, Kakashi is a former member of Anbu. This gives them a special connection and relationship. Sai calls Kakashi “senpai,” which essentially means “senior” in Japanese. This is a sign of respect and an acknowledgment of Kakashi’s experience as a ninja. Sai is also determined to one day fight Kakashi, likely as a chance to prove his worth as a ninja and to show how much he’s learned, improved, and grown in strength.
8 His Personality
Because of Sai’s training with Root, he has spent most of his life not really in touch with his own emotions. He’s been trained to push them down and ignore them.
Even as he learns to get back in touch with them, he still retains some of his training and some of the personality traits that came out of this. Specifically, he’s very submissive and obedient, willing to take orders and obeys them without question.
7 His Brother Shin
When Sai was young, he did have a person that he considered his brother named Shin. They were both a part of the Root division of the Anbu, and they were both therefore trained to feel no emotion and not have personal relationships. But they did grow close despite that and had an almost fraternal relationship. Danzo told Shin and Sai to fight to the death to fully kill their emotions, but because Shin was already dying of an illness, he told Sai to tell Danzo he won.
6 Pays Attention To Detail
One of the big qualities that brings a great deal of help to Team Kakashi is the fact that Sai’s training and quiet personality has allowed him to become very good at noticing details. He is able to see through tricks in battle and support his teammates by noticing dangers that they haven’t. Beyond that, he’s a good friend because of this. He notices when people are lying and how people are truly feeling, which allows him to quietly support them, even if they’re not being honest with him.
5 Wants To Rediscover His Emotions
Spending time with Naruto and Sakura has made Sai realize that having emotions is a special part of being human. He realizes that they’re so close and have so many important relationships because of the way that they feel and express their feelings with each other. As he becomes closer friends with them, he becomes determined to rediscover his emotions for himself so that he can have the same kinds of relationships that they do.
4 Speaks Without Thinking
Since he hasn’t spent a lot of time among other people or with friends, Sai isn’t always the most sensitive to other people’s feelings. He thinks that being honest is the most important thing he can do as a friend, and at first, he doesn’t really understand the difference between being honest and being rude.
He has to learn that sometimes being kind means not telling everyone exactly what he means every time he has a thought.
3 Has Trouble With Friends
Because of his training with Root, he doesn’t really have a good understanding of how friendships work. He has been trained to not think too much about other people or to consider how bonds between people form and why they’re important since having bonds makes it more difficult to get a deadly job done, especially when loved ones can die in the process. It’s a point of contention between him and Naruto since Naruto’s feelings about Sasuke are so strong and Sai doesn’t really understand why.
2 His Hobbies
It’s hard to think about any of the characters in Naruto really having hobbies. All of the characters spend so much time doing missions and training that it’s difficult to imagine that there’s any free time for them to do anything for fun or relaxation. But Sai actually has a couple of hobbies, though it is still pretty difficult to imagine him finding the time to do them. As a pastime, he likes to draw and do calligraphy.
1 His Wife
Despite the fact that he actually thinks that she’s ugly the first time he meets her, Sai ends up marrying Ino, and they have a son together named Inojin, which is revealed in the final chapter of the manga. The most interesting thing about their relationship, besides their rocky start, is the fact that Sai actually takes Ino’s name after they get married. He is the only male character in the series to do so.