Sai

is one of the main supporting characters of the series. He is a young ninja from Root who specializes in techniques that uses ink. He replaces Sasuke Uchiha in Team Kakashi.

Background
Sai was orphaned as a child and recruited into Root, a secret branch of the ANBU. 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. Eventually, his "brother" died of an unnamed illness, and Sai's Root training suppressed most of the memories he had of his brother. Before Shin's death, Sai was making a picture book that would depict all the opponents that they faced and illustrate the feelings that they shared for each other. Sai's and Shin's portraits are located at opposite ends of the book, and in the center pages would be a picture of both him and his brother holding hands. He had forgotten that this was his intention, but after bonding with Naruto Uzumaki he remembers and is able to complete the book, causing Sai to give the first genuine display of emotion in a long time: a smile.

Appearance
Sai has short ink-black hair, and extremely pale skin. He usually is seen carrying a small backpack with his brush, scrolls, and ninja ink. He wears a black midriff shirt similar to Fū and his partner, Torune most likely showing his allegiance to Root. He also carries a tipless tantō on his back. He had Danzō's curse mark on the back of his tongue until Danzō's death, which caused it to disappear.

Personality
When first introduced, Sai was distinguished by his 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.

After spending more time with Team Kakashi, Sai comes to appreciate bonds, particularly the bond that exists between Naruto Uzumaki and Sasuke Uchiha. This causes him to break out of his emotionless shell and he starts to remember the times he had with his own "brother." In doing so, Sai was able to start giving genuine smiles. Wanting to experience personal bonds for himself, Sai sets out to make as many friends as he can. However, since he is learning most of this out of books and by trial and error, he often accidentally ends up offending people with his nicknames and conversation. He has come to develop his own, more pleasant, and thoughtful personality, while showing signs of more emotion, such as enthusiasm and occasionally nervousness. After his first time with Team Kakashi, Sai is seen being friendly towards others, helping companions when they need it, referring to peers kindly, and having fun in social situations.

Sai is very observant, and is always focused on his missions. He pays much attention to detail, allowing him to notice if something is not as it appears or should be, as shown from how he easily sees through Yamato's tricks. This strong awareness seems to span beyond the trials of duty, as Sai was later quick to understand the nature of Naruto's inner burden, stating that he shared a similar fate. What he failed to understand however, was that Naruto was not trying to save Sasuke just for Sakura and that the village's troubles were not burdened entirely on him. He seems to hold Naruto in high regard and seems to overlook some other aspects of the whole picture.

Abilities
As a member of Root, Sai is a highly capable ninja, considered by Danzō himself to be the strongest member of his generation. Danzō had faith in Sai's abilities as not only he terminated his targets in previous missions, but to kill a powerful shinobi Sasuke Uchiha. Sai's most notable talent is his skill as an artist, and he has claimed to have drawn thousands of pictures. Despite the great quantity and magnitude of the things he has drawn, he has never given one of his works a name, his lack of emotion making it impossible for him to form a significant enough attachment to his art to give titles. Even so, Sai's drawing ability is also the source of his jutsu, known as Super Beasts Imitation Picture.

To be able to execute his Super Beasts Imitation Picture technique, Sai carries around a specialized custom scroll to draw on, the scroll's roller has compartments for Sai's ink brush and to hold a supply of ink. In the 'Three-Tails Arrival' arc, Sai is seen leaving a supply store where he gets his ninja ink, he says that the ink from that particular store is the ink that works best for his Super Beasts Imitation Picture techniques. By infusing his chakra into the ink beforehand and drawing objects with a brush on his scroll (something he can do very quickly), Sai is able to bring his creations to life by animating the ink directly off the page. These creations grow to life-size once they have been brought to life--similar to Deidara's Exploding Clay constructs.

Sai typically creates giant birds for long range transport, and lion-like monsters for attack, or objects like umbrellas for everyday use. He can also make copies of himself for reconnaissance. For discreet communiques when he is undercover, Sai is able to turn the words he writes into small animals, allowing them to travel to their intended target unnoticed. Sai is otherwise skilled in close-quarters combat being able to capture Yamato during a practice, protect Naruto from a seemingly deadly attack from Sasuke, disable Kabuto, and take out several Sky ninja in the second Naruto Shippūden film.

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.

Twelve Guardian Ninja arc
In the anime, Team Kakashi is sent on a mission to the Fire Temple. There they learn about one of the Twelve Ninja Guardian corpses being stolen, and are assigned to retrieve three more stolen Ninja Guardian corpses. They follow a trail to a grassy field, only to be ensnared in the enemies' trap, causing the entire terrain to transform into a rocky canyon. After being separated from his team, one of the tomb robbers, Fuen, plants a tracker on Sai and begins targeting him with several traps. Eventually, Sai discovers the tracker and places it on an Ink Clone to deceive Fuen. While failing to defeat Fuen, he managed to shake her long enough to go in search of his teammates.

He later finds Sakura in time to save her from being attacked by a giant spider. Sai's arm is broken in the process, but Sakura is able to heal the major damage. He also showed emotion (most likely for comic relief) when Sakura gave him the antidote for the spider's poison by jabbing a needle into his arm. He was forced to take a temporary leave until his arm fully healed, and in the meantime was replaced by Sora. Despite his injured status, Sai still proved to be of use; when Asuma was having difficulty battling against Kazuma, Sai snuck up on Kazuma with one of his ink snakes and restrained him. Once he gets better and Sora leaves the team, Sai asks if he can be Sora's friend before he departs.

Hidan and Kakuzu arc
Sai begins visiting the Konoha library to read about relationships in the hopes of making some for himself. In the anime, this begins before and continues throughout the Twelve Guardian Ninja arc. When he reads that nicknames are a good way to make friends, Sai makes the mistake of using nicknames that describe how he actually sees a person. When calling Sakura "ugly" earns him a beating, he concludes that women like to be called the opposite of what is true. To that end, he calls Ino Yamanaka "gorgeous", something that receives another beating from Sakura.

Sai and the rest of the team are later sent to provide backup for Team 10 during their battle with Akatsuki. Because Shikamaru Nara was separated from the rest of the group, Sai and Sakura were sent as backup for him, 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 get back. Sai, to improve their friendship, feeds Naruto, angering Naruto because he had wanted Sakura to feed him. Neither has their way when Kakashi arrives to feed Naruto instead.

Three-Tailed Beast arc
In the anime, Team Kakashi is once again sent to provide backup, this time for Team 8. Because the mission might lead to finding Sasuke, Naruto is not to be told about or take part in the mission. When he meets with Naruto he tries to use what he learned from a book to successfully lie, but to his own shame reveals the truth about the mission. Once they set out, Sai is tasked with finding Team 8. When they arrive at the location, they assist Team 8 in fighting Guren. During the fight, Sai distracts Guren while Naruto rescues Hinata.

The two teams then begin pursuing Guren's forces, only to become distracted by a huge tidal wave. Upon recovering, Sai and Hinata discover that it is the Three-Tailed Giant Turtle. After receiving orders to seal the beast, Sai is assigned to prevent anyone from interfering. When he initially proves unsuccessful in this regard, he uses his ink creations to scout a wide area so that he can have proper warning of a future attack. Though he is soon incapacitated, he is able to alert Kakashi to an impending attack. Once Guren's team is finally dealt with and Sai recovers, he once again helps protect the sealing team.

Hunt for Itachi arc
Sai has a diminished role in later arcs. As member of the eight-man squad assigned for the search for Itachi and Sasuke, he just remains as a tracking member team rather than employing any direct action to the mission. He is part of the 8 shinobi that confront Tobi, the weird and funny Akatsuki member that tried to prevent all of them to intervene in the Uchiha brothers' fight.

Six-Tailed Beast arc
In the anime, Sai and the rest of his team are given little time to grieve over their failed mission. Tsunade sends Katsuyu to them with a new mission to help protect the near-extinct Tsuchigumo clan from bandits who are trying steal a dangerous forbidden jutsu. Upon arriving at the clan’s base, it was discover to already have been attacked. The former clan leader’s granddaughter Hotaru managed to escape before the attack with the clan jutsu. Sai, along with Yamato and Naruto, find her in the forest with a mysterious man named Utakata who soon leaves after he deems them capable of protecting Hotaru. Initially, Hotaru refuses to accept the Konoha-nin’s help, but they are able to trick her into accepting it by having Sai create countless big leeches to rain on top of her, promising to keep her safe from them.

They manage to safely get Hotaru to her village, but Naruto refuses to leave yet, feeling something was wrong with the village’s reaction to Hotaru’s return. Naruto’s suspicions soon prove correct as Hotaru is attacked by the bandits and forced into the forest again. Sai, Yamato, and Naruto go after her, and find her being held hostage by Mist Hunter-nin who are attempting to subdue Utakata. After a brief struggle and learning that the Hunter-nin are after Utakata, Yamato steps forth and offers a deal with Hunter-nin captain, not wanting to start up a war between their nations as their respective missions have nothing to do with each other. Yamato convinces them to leave Hotaru and Utakata alone until after their mission is complete, then the Hunter-nin will be left alone to pursue Utakata.

Later, the shocking truth is revealed that Hotaru has the clan’s forbidden jutsu embedded in her back. After learning that Hotaru asked for this to help restore the clan, it is acknowledged the jutsu will only cause more harm and preparations are made to safely remove the jutsu from Hotaru’s back and destroy it. Not wanting to give up just yet, Hotaru insists they find a man named Shiranami‎‎ who should be able to help protect the jutsu, who Naruto goes off to find. Unfortunately, Hotaru runs off after Utakata, who suddenly disappeared. Sai uses his jutsu to desperate search for her and finds her back at her village, as a hostage of Shiranami who is revealed to be the leader of the bandits. Sai and the others arrive in time to help Naruto and Utakata who are being attacked by possessed villagers. They hold off the villagers while Naruto and Utakata go on to save Hotaru.

Invasion of Pain arc
During the invasion of Pain, he is away with Yamato and Anko Mitarashi, tracking down Kabuto Yakushi. He seemed to use a special tracking jutsu to not be noticed by Kabuto. Anko even congratulated him for that. They stopped the search just after a surprised Yamato tells the group that Naruto has reached the six-tailed form of the Nine-Tails.

Five Kage Summit arc
After learning that his master was appointed to become the Sixth Hokage, Sai immediately went to Danzō for new instructions. After being ordered to watch Naruto carefully, Sai hesitantly asked Danzō his plans for Naruto, worrying about his friend's well-being. This did not go unnoticed by Danzō. Later, Sai was confronted by Naruto and Sakura.

The two asked Sai to reveal all he knew about Danzō. Unfortunately, Sai revealed he was unable to talk about such things because of the Cursed Seal Danzō placed on all members of Root. If he ever talked about Danzō or Root, he would be permanently paralyzed and unable to talk. When Sakura comments on how Danzō could treat his own subordinates through this manner just to ensure security, Sai defended him by explaining that Danzō and his entourage have long since been protecting Konoha through any number of foul deeds, and it was through such methods that he secured Konoha's existence. He did however reveal to be surprised and dissatisfied with Danzō's decision to kill Sasuke. Quickly afterwards, Sai and his friends were attacked by two of the three Kumogakure ninja sent by the Fourth Raikage. They ordered for information on Sasuke, who they revealed to now be a member of Akatsuki and expressed their desire to kill the latter. This greatly shocked Sai and his friends. When Karui insulted Sakura of what she is to Sasuke, Sai defended her and commanded Karui not to put too much pressure on his friends.

Later, he witnessed Karui beating up Naruto, to which he soon interferes, stopping another blow aimed at the already pulverized Naruto. Naruto tells Sai to stay out of his fight, but Sai refuses. He tries to convince Naruto that Sasuke isn't worth getting beat up over and tells Naruto that Sasuke has done nothing but hurt him. He helps Naruto to find Kakashi and Yamato and then aids Naruto in cleaning and wrapping up his wounds from the fight. Naruto thanks Sai for the latter's concern for him. It is revealed that Kakashi knows about Sai's current mission to keep an eye on Naruto. He queries to Kakashi as to why Naruto and Sakura are still going to far to help Sasuke when the missing-nin seems bent on continuously hurting his two friends, to which Kakashi replies, "I think you already know". It also appears that Danzō has begun to lose faith in Sai; though he does say that he doesn't think Sai will betray Root, he has some of his men watch Sai "just in case". Before Kakashi leaves with Naruto for the Land of Iron he tells Sai that he trusts him and then disappears leaving Sai with a strange feeling. After Naruto's departure, recalling Naruto's feelings for Sakura and some inner conflict, Sai decides that he can no longer act as a mere spectator and approaches Sakura on the matter.

Sai tells Sakura that Naruto truly loves her and that he feels that she has cursed him the same way Sai himself is by Danzō by holding him to his promise to bring Sasuke back and he also tells Sakura that she is hurting Naruto like Sasuke does. He knows Naruto is not only saving Sasuke because of the promise, but thinks everyone should stop relying on Naruto. Sai notes that he is aware that Naruto seeks to save Sasuke for his own sake as well, but is also filled with anger.

Sai is seen with Lee, Sakura, and Kiba heading to the Land of Iron to confront Naruto, he asks Kiba to start tracking Naruto as soon as they arrive. After finding him, he looks on stoically as Sakura talked to Naruto. As the group leave, a second Sai watches the team depart some distance away. After making sure that Sakura's group has left, the clone approaches Naruto, to tell him the truth that Sakura couldn't bring herself to tell. Sai explained that the rest of Konoha 11 has decided to kill Sasuke. As his actions will lead to war with the other countries and one person is not worth the risk of total war. He then presumed that Sakura plans to kill Sasuke herself because she feels guilty and that she is still in love with him, through Sai's words, caused Naruto so much pain over the years. Sai becomes involved with a plan with Kakashi, and Yamato to overthrow Root's influences.

As Kiba finds Sasuke, Sai reveals Sakura's plans to knock everyone out to fight Sasuke herself. Sai then stands firm on his promise to Naruto and Kakashi to stop his teammates from foolishly taking on Sasuke alone. He also readies himself as Sakura prepares to fight him in order to get to Sasuke. Sai refuses and unleashes a bunch of ink snakes. As Lee and Kiba attack, Sai is able to subdue them with his snakes. Unfortunately, Sakura unleashes smoke bombs that knock out her teammates and then goes on to find Sasuke. Before fainting, Sai gives the new information to his clone who warns Kakashi of Sakura's continued pursuit. Kakashi follows the final directions from the clone to Sai and the others, and moves them to a safer location before going after Sakura.

Fourth Shinobi World War arc
After waking up from Sakura's smoke bomb, Sai started arguing with Naruto about how simple-minded and slow he is. ANBU from Root came to the team and Sai confirmed to them that Danzō has died. The proof was the cursed seals Danzō placed on them when they first joined Root had disappeared. He also mentioned that Root had to have a long talk with the new Hokage, Kakashi.

Shippūden The Movie 2: Bonds
Sai, due to his ability to create flying mounts for himself with his Super Beasts Imitation Picture Technique, served a double function as a scout and first counterstrike against the Sky-nin attackers by using taijutsu to jump and wreck different Sora-nin wing sets. He admits, soon after, that he is actually bored with the incompetence of the sky nin.

Shippūden The Movie 3: Inheritors of the Will of Fire
Although not officially given a mission, after recovering from previous injuries, Sai pursued the Konoha Eleven on their way to Hiruko's base. Temporarily blinding San with a flashbang, he picked up Naruto and Sakura in order to get them ahead of the following teams, leaving Shikamaru and his teammates to deal with San.

Trivia

 * It was commented on by Sakura, Ino, and Naruto that Sai resembled Sasuke physically. However, Sai and Sasuke had totally different personalities and Sai has extremely pale skin and short hair compared to Sasuke.
 * As an ANBU member, Sai refers to Kakashi as his Senpai out of respect.
 * According to the third Naruto databook:
 * Sai's hobbies are drawing and calligraphy.
 * Sai wishes to fight Kakashi Hatake.
 * Sai's favorite food is momen tofu, while his least favorite is mitarashi dango.

Quotes

 * (To Sakura) "I've drawn hundreds, maybe thousands of pictures so far... other pictures have the situation at the time, and the artist's feelings... like portraits have the person's name... but don't pictures usually have titles...? To be more precise, even if I try to give them titles, I just can't do it. I don't feel anything... they don't put me in mind of anything."
 * (To Kabuto) "If people change... then so can I. But some things never change. Bonds. I'd like to learn more about them."
 * (To Naruto, Sakura and Yamato) "Sai is the name I was given for this mission... I'm nobody. I am a tool for Lord Danzō. I don't exist."
 * "...I don't have feelings."
 * (To Sakura) "A smile can get you out of a tough situation, even if it is fake."
 * (To Naruto) " I read it in a book... People always smile around the people they like. And you're always smiling at her. Did you tell her how you feel?"