Village: Leaf Village
Personality: When first introduced, Sai was distinguished by total lack of emotion which he often masks with a false, cheerful, yet transparent facade. After much mental conditioning and training while in Root, Sai had suppressed almost all of his emotions, laying all of his loyalty to whoever commands him, and thus making it easier for him to accomplish dangerous, unpleasant, or unethical missions. Due to this training, both his own lack of social experience and personal initiative cause for Sai to have great trouble in understanding how bonds and friendships between people can motivate others. He often showcases this confusion after thinking about why Naruto would go so far to save Sasuke, even though Naruto had not been ordered to do so.
Bio: Sasuke and Sai arc:
Sai was assigned to join Team Kakashi by his superior Danzō to assist in meeting with a spy in Orochimaru's ranks to find out about Sasuke Uchiha. Sai is confrontational with his new teammates, questioning Naruto's manhood and insulting Sasuke. The latter causes Sakura Haruno to punch him in anger. As they continue on to the meeting point, Sai questions why Naruto is loyal to a traitor like Sasuke, to which Naruto said he's not a traitor, but a friend.
Upon reaching the designated meeting place, Yamato went ahead disguised as Sasori so that he could meet the spy. When the spy, Kabuto Yakushi, arrived with Orochimaru to kill Sasori, Sai, Naruto, and Sakura were called in for help. When Naruto and Orochimaru begin fighting, Sai leaves the rest of the team to begin his real mission. He observed Naruto's fight with Orochimaru, unconcerned with the danger he left Yamato and Sakura in, and approaches Orochimaru after he had repelled Naruto with a proposition from Danzō. Orochimaru accepted, and Sai accompanied him and Kabuto back to their hideout.
Once arriving at Orochimaru's hideout, Sai was introduced to Sasuke, who had been training under Orochimaru for the past two-and-a-half years. When Sai mentioned that he might get along better with Sasuke than he did with Naruto, Sasuke fixed him with a stare, startling Sai due to the amount of fear it gave to his emotionless self. He was led to his own room afterwards by Kabuto, who locked Sai in upon leaving. Soon afterwards, Team Kakashi tracked Sai down and confronted him about his real mission. Caught, Sai explained that he had been assigned to ally with Orochimaru on Danzō's behalf so that the two may join forces in destroying Konohagakure.
Disgusted by the ramifications of this plan, Team Kakashi restrained Sai before setting out to find and retrieve Sasuke. Sai, however, doubted their success, stating that Sasuke no longer cared about them. Naruto, in response, stated that he used to hate Sasuke, but over time he had formed a bond with Sasuke through their shared experiences, and as such he would do whatever it took to bring Sasuke home. Naruto's dedication to retrieving Sasuke struck a chord with Sai, who was left without words as a result. When Kabuto arrived and freed Sai, Sai instead helped to capture Kabuto, hoping to accompany Naruto to find out more about bonds.
Naruto and Sai split away from Sakura and Yamato to go looking for Sasuke. They are soon found by Orochimaru, and Naruto distracts him so that Sai can have a chance to scout on ahead. When Orochimaru retreats and Naruto reunites with Sakura and Yamato, Yamato goes through the belongings that Sai left behind. In doing so he discovers Sai's actual mission: to kill Sasuke as a traitor to Konoha. Team Kakashi races through the base to find and stop Sai, but Sai has already found Sasuke. Sai, however, truly has had a change of heart, and tries to capture Sasuke in order to protect his bond with Naruto.
Irritated by Sai's reasons for bothering him, Sasuke attacks Sai, drawing the rest of the team to their location. When they find out what Sai was trying to do, they all team up to restrain Sasuke. Although Sai is able to land a successful attack, Sasuke's abilities are too much for them and he prepares to kill them all. He is stopped by Orochimaru and Kabuto, who convince him to spare the team before leaving. Defeated, Team Kakashi returns home. Sai requests that he be allowed to stay a part of the team and, with Danzō's approval, begins spending time with his new friends.