If Naruto's friends or loved ones are threatened by the ANBU, either directly or indirectly. For instance, if the ANBU's actions put Sakura or Kakashi in danger without just cause, Naruto would be likely to turn against them. He's very loyal to his friends, and any threat to them would be a strong motivation for him to take action against the ANBU.
One possible reason could be the intense and often dark nature of Anbu missions. Naruto might be exposed to a lot of death and destruction, which could lead to his depression. For example, he could witness the killing of innocent people during a mission and feel powerless to stop it.
Another reason might be due to a personal vendetta against someone in the village. If someone in the village wronged them deeply, like a powerful figure who abused their power, Naruto and Sakura might take actions that seem like betrayal to the village in order to seek justice. However, they would likely believe they are doing the right thing in the long run.
In some fanfictions, Naruto might leave the Anbu due to internal conflicts within the organization. There could be corruption or power struggles. Naruto, being the idealistic character he is, would not want to be part of such a messed - up system. He might have discovered some dark secrets about the Anbu that made him decide it was not the place for him.
Another factor could be the toll it took on his mental health. The ANBU often deals with dark and difficult missions. Naruto, with his positive and somewhat naive outlook on life, might have been affected more than others. He could have started showing signs of not being able to cope, and as a result, they forced him out to protect him from further harm.
Another reason might be related to their different ideologies within the ANBU. Naruto may have believed in a more collaborative and friendly approach within the organization, while Sasuke might have been more focused on individual achievement and power. This fundamental difference could lead to Naruto hating Sasuke in the fanfiction.
Well, in fanfiction, the author often likes to create complex and unexpected plot twists. It could be that Naruto's loyalty to his own values and beliefs clashes with the goals and ethics of Rias, Sona, and Ravel. For instance, Naruto may be against certain practices that they engage in, like how they handle power or deal with other groups. This ideological difference could lead to their betrayal. Also, there could be a love triangle or some sort of relationship drama involved. If Naruto is involved with someone they all like or if there are misunderstandings in relationships, it could spark the betrayal.
In some fanfictions, Naruto's life in Anbu could lead to a significant change in his character. He may become more withdrawn and brooding as he deals with the darker side of the ninja world that Anbu often encounters. His relationships with his friends might also be strained as he has to keep parts of his Anbu life a secret. This could create a lot of drama and tension in the story.
Well, it could be that Naruto's friends are influenced by a dark power. This power could twist their perception of Naruto, making them see him as a threat instead of a friend. Or perhaps there's a prophecy that Naruto is supposed to be the cause of some great disaster, and his friends, in an attempt to prevent it, decide to betray him. It's also possible that a new character enters the story and sows seeds of discord among them, leading to the betrayal.
It could be Itachi. Even though Itachi has his own complex past, he is highly skilled in Anbu - like operations. He could show Naruto the ropes of the Anbu world, teaching him how to analyze situations quickly and make tough decisions that are often required in Anbu missions.
One possible reason could be jealousy among his peers. Maybe someone was envious of Percy's skills or popularity and spread false rumors about him, leading to his betrayal. For example, if Percy had a special power or was favored by a certain group, others might feel left out and decide to turn against him.