Sai was orphaned as a child and recruited into Root, a secret branch of the Anbu under the leadership of Danzō Shimura. There, he was raised and conditioned to have no personality, personal connections, or a name; "Sai" being given to him for the purposes of joining Team Kakashi. Though largely successful in this regard, Sai retained an interest in art. When Shin, an older Root member, discovered Sai's drawing ability, he encouraged Sai's talent and they became very close.
Over time, Sai came to think of Shin as an older brother and looked up to him. Unfortunately, the final step in Root training called for the two to fight to the death to eradicate all remaining emotions. Before that happened, however, Shin died of an unnamed illness and Sai's Root training suppressed most of the memories he had of him. In the anime, Sai and Shin were forced to fight by Danzō but Shin, knowing that he was dying anyway, told Sai to report to Danzō that he had killed him in battle. Before dying, Shin told his brother that he had to suppress his feelings, and to live for the both of them.
Before Shin's death, Sai created a picture book that would depict all the opponents they faced and illustrate the feelings that they shared for each other. Sai organised the book so that his and Shin's portraits would be located at opposite ends of the book, and in the centre pages would be a picture of them holding hands. Some time after the loss of Shin, Sai forgot that this was his intention, and the picture book was left unfinished, though he could never bring it upon himself to discard the book.
During his time in Root, Sai was ordered to eliminate a large number of individuals that posed a threat against Konoha. At the time he was assigned to Team Kakashi, the last assassination he performed was of Unmo Samidare. In the anime, an attempt to gain a powerful fūinjutsu after seeing the Third Hokage sacrifice his life in an attempt to defeat Orochimaru, led Danzō to supervise Sai while he learned how to use the Sealing Technique: Tiger Vision Staring Bullet, noting that it would be dangerous as he would have to use "emotional energy" in order to make the technique stronger. Sai struggled greatly with this endeavour as it conflicted with his training and, consumed by negative emotions, his training was seemingly left incomplete.
Tenchi Bridge Reconnaissance Mission
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 was confrontational with his new team-mates upon their first meeting, exasperating both Sakura and Naruto. On their way to the rendezvous point, Sai once again aggravated them, questioning Naruto's manhood and insulting Sasuke. The latter caused Sakura Haruno to punch him in anger. As they continued on to the meeting point, Sai questioned why Naruto was loyal to a traitor like Sasuke, to which Naruto stated he was 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 began fighting, Sai left the rest of the team to begin his real mission. He briefly observed Naruto's fight with Orochimaru, unconcerned with the danger he left Yamato and Sakura in, and approached Orochimaru after he had repelled Naruto with a proposition from Danzō. Orochimaru accepted, and Sai accompanied him and Kabuto back to their hideout. Once arrived 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 Naruto, Sasuke temporally traps Sai within a genjutsu which startles Sai to the ground due to the amount of fear it gave 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. Having been 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 also 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 them capturing 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 were soon found by Orochimaru, and as a result, Naruto distracted him so that Sai could have a chance to scout on ahead. When Orochimaru retreated and Naruto reunited with Sakura and Yamato, Yamato went through the belongings that Sai had left behind. In doing so he discovered Sai's actual mission: to kill Sasuke as a traitor to Konoha.
Team Kakashi raced through the base to find and stop Sai, but Sai had already found Sasuke. Sai, however, truly had a change of heart, and instead, tried to capture Sasuke in order to protect his bond with Naruto. Irritated by Sai's reasons for bothering him, Sasuke attacked Sai, drawing the rest of the team to their location. When they found out what Sai was trying to do, they all teamed up to restrain Sasuke. Although Sai was able to land a successful attack, Sasuke's abilities were too much for them and he prepared to kill them all. He was soon stopped by Orochimaru and Kabuto, who convinced him to spare the team before leaving. Defeated, Team Kakashi returned home. Sai requested that he be allowed to stay as a part of the team and, with Danzō's approval, began to spend time with his new friends. Upon returning to Konoha and failing their mission, Sai began reading about relationships in the hopes of making some for himself.
Twelve Guardian Ninja
In the anime, Team Kakashi are sent on a mission concerning the Fire Temple. When the other party didn't meet the group, they decided to split into two groups. He stayed behind with Naruto while Yamato and Sakura went to search for the monks. His weird actions to try and build a stronger friendship with Naruto creeped him out and Naruto fled away from him. After re-grouping with Yamato and Sakura who found the monks, Sai witnessed Sora, a monk-in-training, fighting Naruto. This turned out to be a misunderstanding on the behalf of Sora thinking Naruto was trying to invade the temple.
After clearing up the confusion, the monks led Team Yamato to the Fire Temple. Upon reaching the temple, the monks explained to the team the situation regarding the sacred tombs' mysterious disappearance. News that another tomb was robbed reached the temple and Team Kakashi, accompanied by Chiriku and Sora, moved out to find the perpetrators. They soon spotted four other tombs moving across a field by themselves, heading up a cliff where four ninja lied. Fudō, one of the enemy ninja, quickly used an earth technique to create a rocky canyon maze, which separated Team Kakashi and Sora. Using an ink bird he tried to escape but was ultimately trapped inside. He was confronted by Fuen who mocked him for not being able to escape. Sai aware that the enemy knew the area, attempted to retreat and plan. Though he did get away, the enemy had the blue prints to the area and knew exactly where he went off to and tried to kill him. Some time after, he found and saved Sakura from a surprise attack from a giant spider. He managed to kill it, however, getting his arm injured in the process and Sakura tended to it. After the two had met up with Yamato, they found Naruto being drained of his chakra by a kiss from Fūka. They tried to help but were trapped by Fuen and Fudō. The cave soon collapsed and everyone scattered to safety.
When the group returned to the village, Sora went with them. While Sai left to take a rest, Naruto introduced Sora around the village per Sakura's request. Later, Sai, looking through the hospital window, saw that the village was being attacked by a technique used by Fudō and his fellow members. After sneaking out, he helped Asuma fight Kazuma, enabling Asuma to finish him off. The invaders were dealt with and Sora departed from Konoha.
Akatsuki Suppression Mission
Sai and the rest of team Kakashi were later sent as backup for Team 10 during their battle withAkatsuki. Because Shikamaru Nara was separated from the rest of the group, Sai and Sakura were sent to his aid, though upon arrival they found that Shikamaru had already defeated his opponent. Sai returned with everyone else to Konoha, having not taken part in the battle. Because Naruto was injured during the battle, he has difficulty eating when they got back. Sai, wanting to ameliorate their friendship, attempted to feed Naruto which angered him since he had wanted Sakura to feed him and Sai had interrupted her doing so. Neither has their way as Kakashi himself took up the task of feeding Naruto instead.
In the anime, Sai was placed on Team One along with Kakashi, Shino and Naruto. His team's duty was to fight any enemies who closed into the area so they wouldn't disrupt the sealing process for Team Three, who were going to seal the Three-Tails. After he had introduced himself to Shino, he found that Shino had a bit of a grudge towards Naruto, since it turned out that though Sai only knew Naruto for a few month and knew more about Naruto, much more than he did. Sai's team ran into Guren andGozu. As the battle between them commenced, Sai soon took on Gozu alone. Sai managed to temporarily restrain him with his ink snakes but with his brute strength broke free shortly after. The sealing is disrupted and they were forced to retreat and devise another plan.
After he and the other Konoha-nin recuperated, he mistakenly got in between Sakura and Ino's bickering, and by being oblivious to the situation, repeated the names they yelled at each other thus getting himself punched by both of them. He and the others at some point find out that the young boyaccompanying the enemies can partially control the beast. They eventually find him unconscious and take him with them. After Yūkimaru was treated by Sakura and Ino, Kakashi decided to use him to conjure up the beast to try sealing once more. After that Sai was tasked with bringing him to an secure place. However, he got attacked by some of Guren's men and despite his efforts, he was defeated and Yūkimaru was captured. Later, he battled foes who were merged but were crushed by the Three-Tails on its ramapage. Having failed to seal the beast again, they returned to their village and left the rest up to the leaf Anbu.
- Capture Sasori's Spy, and bring him back to the Leaf. Hopefully gathering intel on Orochimaru, and Sasuke Uchiha.
- Kill Sasuke Uchiha.
- Go and backup Team Kurenai looking for Orochimaru's Hideout.
- Your Mission is to rescue the kidnapped Hanabi Hyuga. Shikamara you will lead this 4 man team. I am also allowing Hinata Hyuga to join.
- Ink Clone
- Ink Fish
- Sealing Jutsu: Crouched Tiger Bullet: But be careful releasing your emotions can make you subtiple to the effects of your Negative feelings. And that can be very dangerous. You sub come to your Negative Feelings. They are consuming you. You must assimilate the mass of Negative feelings you have pent up within you. And train carefully to use them. This Jutsu is the reason why I raised all of you from the time you were young. Keep going until you gain complete control over your emotions. Learn to release all your negative feelings you have to master them Sai.
- A Sealing Jutsu that becomes more powerful when i release my emotions. But those emotions don't have to be Negative ones from Anger or Sadness.
If you hadn't fallen for the Captain's obvious trick...he never would have found out I was hiding somewhere else.And perhaps I might have been able to capture him with even less trouble than I had.Why even bother masquerading as me...if you're going to reveal yourself almost immediately by using one of your own jutsu?Because of your mistake, the Captain was able to see through our strategy and use a Substitution Jutsu to escape into the forest.Well, then...if you knew it was a Substitution why didn't you break your jutsu right away?It's impractical to fight while covering for someone who's lost his cool. I simply considered what would best ensure mission success and acted accordingly.
- Sai becomes Sasuke's permanent replacement as a member of Team Kakashi until Sasuke returns.
- The picture that Sai draws of himself joining Naruto and the others, he names "Comrade".