It could also be related to his unfulfilled dreams. Naruto has big dreams for the village and for peace. But as he progresses, he might realize that achieving true peace is far more difficult than he thought. The gap between his ideals and the reality might be leading to his secret depression.
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.
A plot could involve Naruto being secretly depressed because he realizes the cycle of hatred in the ninja world may never end. He's fought so hard to bring peace, but new threats keep emerging. He starts to question the purpose of his efforts and falls into a deep depression. He may keep this hidden from others because he doesn't want to discourage them or seem weak, but it slowly eats away at him.
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.
One possible reason could be the loss of his friends. In the Naruto universe, his friends are his most precious. If he were to lose some of them in a really tragic way, like Sasuke turning truly evil and being killed while trying to destroy the village, it could plunge him into severe depression. Another reason might be the weight of his unfulfilled dreams. Naruto has always dreamed of a world of true peace, but if in fanfiction he constantly faces setbacks in achieving this, like new wars breaking out despite his efforts, it could lead to depression.
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.
There are several potential reasons. It could be a result of a psychological experiment gone wrong. Some fanfictions like to play with the idea of Naruto being a test subject, and this could lead to his emotions being numbed. Another aspect could be related to his role as a leader. In some fanfictions, to be a strong and effective leader, he might believe he has to hide his emotions. Additionally, it could be a reaction to the expectations of others. If everyone expects him to be a fearless hero all the time, he might start to suppress his true emotions to meet those expectations.
Well, Naruto has always been there for Sasuke in the original story. In fanfiction, Fem Sasuke might secretly like Naruto because she sees his loyalty. He's constantly trying to bring Sasuke back to the right path. This loyalty could translate into a deeper affection in the fan - created stories.
In fanfiction, Naruto could be depressed after the war because he realizes that the world he fought for is still full of problems. The shinobi system might still be corrupt in some ways, and he may feel that all his efforts haven't really changed the fundamental issues. He might also be suffering from post - war stress disorder, constantly reliving the battles and the horrors he witnessed.
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.
One reason could be to protect someone. For example, if there is a threat against a friend or a loved one, she might meet someone secretly to plan a way to keep that person safe without alerting the enemy. It's a common plot in fanfictions where the characters have to be sneaky to outwit their foes.