In the Naruto series , there are a number of ninja whose duties are like the police. They are usually called Anbu and have a special mission, which is to carry out tactical operations and maintain village security.
The task of the Anbu is indeed quite heavy, so that only strong and well-trained shinobi can be elected as Anbu. Through the episode "Kakashi Anbu Hen: Kakashi: Shadow of the Anbu Black Ops" in Naruto: Shippuden , a lot of stories about Anbu are shown, especially the story of Kakashi who has experienced a lot of trauma from his past events.
Throughout episodes 349–361 of Naruto: Shippuden , you can see a series of events focusing on Kakashi's background as an Anbu and the backgrounds of other characters, such as Yamato and Itachi Uchiha.
The story of Kakashi in the Naruto anime when he joined the Anbu
Kakashi joins the Anbu
Kakashi's role as an Anbu is shown in the missions of Yamanaka, Nara and Akimichi. His fathers Ino, Shikamaru, and Chji were sent to complete the Iwagakure treaty mission. The peace treaty meeting took place on the border with the Land of Wind, so the Fourth Kazekage made sure there would be no fights near his country.
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Iwagakure returned and informed the Third Tsuchikage of the events. In Konohagakure, Kakashi still feels guilty for his role in Rin's death. In a meeting with the council, Hiruzen decided to step down in favor of the new Hokage. Danzo suggested Orochimaru, but Hiruzen suggested Minato to become Hokage.
Minato finally took over as Hokage. As Kakashi continued to struggle with his trauma, Minato assigned Kakashi to become an Anbu. You see, Minato believes that Kakashi can kill the opponent very viciously. At Hiruzen's suggestion, Minato ordered Kakashi to supervise Kushina who was pregnant at the time.
When the nine-tailed fox attacked Konoha, Minato and Kushina held it back at the cost of their lives. Kushina told Hiruzen that her son's name was Naruto and begged to protect him. Hiruzen continued Minato's duties as Hokage and Danzo invited Kakashi to be part of his bodyguard and join the ninja masters of the wood elemental stance.
One day, Danzo planned to kill Hiruzen but Kakashi thwarted his plan. Danzo also allowed Kakashi to escape and believed that his abilities would one day be valuable to Konoha. On the other hand, Hiruzen informed Kakashi of Kinoe's whereabouts, and Kakashi became an Anbu under Hiruzen's command.
Misi Kinoe
Under Danzo's orders, Kinoe and Kinoto set out to retrieve Kakashi's Sharingan. At the same time, Kakashi is sent by Hiruzen to investigate Orochimaru's newly discovered hideout. Kinoe and Kakashi meet each other and agree to work together. However, Kinoe immediately attacked Kakashi to take his eye.
Kakashi begs Kinoe to stop and tells him that friends shouldn't kill each other. Kinoe brought up the fact that Kakashi killed Rin with his own hands. Those words clearly angered Kakashi, pinning Kinoe to the ground, and preparing to attack him with a Chidori. Kinoe turns himself in and tells Kakashi to kill him if necessary.
Itachi joins the Anbu Following Kakashi
After the events above, Itachi joined the Anbu and became the youngest member ever. His father emphasized Itachi's obligation to protect the Uchiha clan. On the other hand, Danzo actually assigned Itachi to monitor the Uchiha.
Hiruzen then sent a team consisting of Guy, Kosuke Maruboshi, and two other ninja on a diplomatic mission to meet the envoy of the Land of the Forest. Then, Danzo sent Kakashi and Itachi as backup in case they were betrayed.
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Konoha was apparently betrayed, so Kakashi and Itachi eliminated the envoy. Guy asks Hiruzen that Kakashi be dismissed from his Anbu duties as he believes it is not good for Kakashi. Then, the Konoha council decided that the Uchiha clan would be placed under surveillance. According to Itachi, the move was expected from the Uchiha clan.
Uchiha clan killed by Itachi
Hiruzen assigns Kakashi to find out who passed the village guard. Itachi reports to Danzo that a coup is imminent. Unfortunately, the Anbu arrived too late to stop him.
The entire family of the Uchiha clan had been killed by Itachi, leaving only Sasuke and Obito. Itachi also warned Danzo not to hurt Sasuke or he would leak information to an enemy country. Itachi also secretly met Hiruzen, informed him of his future actions, and asked to protect Sasuke.
Hiruzen decided not to change the barrier passcode, in order to allow Itachi to enter the village undetected to check on Sasuke. After the incident, Kakashi was expelled from the Anbu and told that he would become a sensei for the genin team.