The strict rules and hierarchy in the Anbu could also be a factor. Naruto may find it difficult to adapt to the rigid command structure. If he is constantly being reprimanded for not following orders exactly as given, or if he feels that his ideas and values are not respected within the Anbu, it could lead to his depression.
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.
Well, in such a fanfiction, perhaps Naruto has just lost Sasuke again and is deeply depressed. The ANBU, seeing his skills and his need for a distraction, recruit him. He starts off being a bit of a misfit in ANBU, not following all the rules because of his independent nature. But as he continues, he starts to understand the importance of their work. He might even form new bonds with his ANBU comrades, which slowly help him come out of his depression.
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.
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.
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.
One possible reason could be the weight of his past. Naruto grew up as an orphan, constantly shunned by the villagers. In the fanfiction, this feeling of isolation might be intensified, making him constantly depressed. Another reason could be the pressure of his goals. He aims to become Hokage but might face numerous setbacks that make him feel inadequate and depressed.
One reason could be that Gaara, being a powerful and complex character, might have a different view on the concept of friendship. If he were to tell Naruto that his friends are only with him out of obligation or because of his status as a hero, Naruto might start to doubt his relationships and become depressed.
Naruto's character would likely become more reserved at first. He'd be constantly fighting his own demons while trying to fit into the ANBU. As he goes on missions, he'd start to learn more about the darker side of the ninja world. This new knowledge might make him more cynical initially, but over time, he could use it to grow stronger. His depression might also fuel his determination to prove himself in ANBU, leading to him becoming a more complex and mature character.
One possible reason could be unrequited love. If in the fanfiction, Sakura continuously rejects Naruto or shows no interest in him, it can lead to his depression. Naruto has deep feelings for Sakura for a long time, and constant rejection can be soul - crushing.
Well, in fanfiction, one reason could be the loss of his friends. Percy has been through so many battles, and if he loses someone close like Annabeth or Grover, it could send him into a deep depression. Another reason might be the burden of his prophecies. He's constantly expected to save the world, and that kind of pressure can wear a person down over time.