Sai

is one of the main supporting characters of the series. He is a young ninja from Root who specializes in techniques that use 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 created a picture book that would depict all the opponents they faced and illustrate the feelings that they shared for each other. Sai organized the book so that his and Shin's portraits would be located at opposite ends of the book, and in the center pages would be a picture of them holding hands. Sometime after the loss of Shin, Sai forgot that this was his intention, and the picture book was left unfinished. But after bonding with Naruto Uzumaki, Sai remembers and completes the book, causing him to give his first genuine display of emotion in a long time: a smile.

Appearance
Sai has short ink-black hair, ink black eyes, 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 and his lack of social experience and personal initiative, Sai has great trouble in understanding how bonds 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 a more genuine, pleasant and thoughtful personality, while also 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 even had enough faith in Sai's abilities to task him with single-handedly killing Sasuke Uchiha. Sai's most notable talent is his skill as an artist, and he claims to have drawn thousands of pictures. Despite the great quantity and magnitude of the things he has drawn, he has never given any 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, which he says 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 training, 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-Tails 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-Tails 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 the invasion, Danzō is made Hokage. He summons Sai before him and instructs him to keep an eye on Naruto. Sai asks why, so Danzō explains that Naruto, having defeated Pain, is the village's hero and thus more popular than Danzō himself. However, he is still the village's jinchūriki and must be kept in check. Sai is satisfied and goes the meet with Naruto and Sakura. The two immediately confront him about Danzō, asking that he tell them everything he knows. Sai says that he cannot, as the cursed seal Danzō placed on his tongue prevents him from revealing anything about Root. Sakura says it is cruel, but Sai explains that it is for the best since Root has done a number of questionable things to protect the village.

Sakura refutes his claim, pointing out that Danzō has ordered Sasuke be killed as a traitor. Sai is surprised, Danzō not having told him that during their meeting. They are immediately confronted by Kumogakure ninja who ask for what they know about Sasuke. Naruto, seeing that this upsets Sakura, volunteers to tell them all that he knows. Sai secretly watches the meeting and how Naruto cannot bring himself to sell out Sasuke. Naruto allows Karui to take out her anger on him. Karui happily accepts and begins beating him up, but Sai steps in once she starts to over do it. When Karui leaves, Sai brings Naruto to Kakashi and Yamato and then tends to his wounds. Naruto asks that Kakashi and Yamato help him find the Fourth Raikage. When they agree, Kakashi requests that Sai defy his orders by not telling Danzō what Naruto is doing. Sai complies.

Sai later approaches Sakura, telling her about what Naruto went through with Karui for her benefit. He surmises that Naruto loves Sakura, and that trying to make her happy, such as bringing Sasuke back to the village, causes him constant pain. Following the Konoha 11's decision to eliminate Sasuke themselves to prevent a war, Sakura asks that Sai help her track down Naruto so that she can speak with him. They find him in the Land of Iron and Sakura tells Naruto that she loves him, so now he doesn't need to bother fulfilling his promise of retrieving Sasuke. When Naruto claims she is lying she leaves. Because she doesn't mention the decision to kill Sasuke, he leaves an ink clone behind to tell them what Sakura did not. The clone also adds that Sakura is likely planning to kill Sasuke personally, and mentions that Sakura is still in love with Sasuke and wants to stop him from sinking any lower.

The ink clone helps Kakashi locate Sakura. The real Sai, meanwhile, stops Sakura from knocking out him and her other escorts, having suspected that she would try to get rid of them so she could fight Sasuke alone. Sakura convinces Kiba and Lee that Sai is a traitor and they start to fight him, but this only makes it easier for her to knock out all three. As the ink clone disperses it warns Kakashi of Sakura's actions. Sai and the others are later woken following the meeting with Sasuke, and as they return home they are met by two Root members. The Root agents ask why their cursed seals are gone, which Sai explains is proof that Danzō has died. He then encourages them to speak with Kakashi.

Naruto Shippūden 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 Sora-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 Sora-nin.

Naruto Shippūden 3: Inheritors of the Will of Fire
Although not officially given a mission, after recovering from previous injuries, Sai pursued the Konoha 11 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 word is "Comrades".
 * Sai's favorite food is momen tofu, while his least favorite is mitarashi dango.
 * Sai has a frank, obedient and submissive personality.
 * In the seventh Naruto Shippūden opening, Sai is shown fighting Asura Path, though in the manga, they do not fight.

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?"