One possible reason could be the intense pressure he feels to protect the village. He might overexert himself in training and accidentally hurt himself. Another reason could be self - punishment for not being able to save someone. In some fanfictions, Naruto might feel guilty about a comrade's death and take it out on himself through extreme training or dangerous missions.
In some fanfictions, Naruto could be under a genjutsu that makes him harm himself. For example, an enemy might have cast a powerful genjutsu on him that distorts his perception of reality, making him think that he needs to do harm to himself in order to achieve a certain goal. Also, if he discovers some dark secrets about his family or the village, it could lead to an emotional breakdown and self - harm.
One possible reason could be the loss of his friends. Naruto values his friends deeply, and if he were to lose someone like Sasuke again, it would be devastating. Another reason might be the pressure of being the Hokage. The responsibilities are huge, and he might feel like he's not living up to the expectations of the village. Also, memories of his lonely childhood could resurface, making him feel sad and alone, leading to him crying himself to sleep.
There are several reasons. He might be afraid of getting too close to people because he's lost someone important and is scared of more loss. It could also be that he's discovered some new power within himself that he doesn't understand and is worried about hurting others if he gets too involved. Additionally, there could be some political intrigue in the village. Maybe there are some people who are plotting against him and he's keeping to himself to avoid being a target or putting others in danger.
One possible reason could be extreme guilt. Maybe he fails to protect his friends in a major battle and feels so responsible that he can't bear it. For example, if Sasuke were to die because Naruto couldn't reach him in time, Naruto might sink into such deep guilt that he sees no way out but death.
Well, it could be a situation where Hinata is trying to protect someone else from Naruto, perhaps believing he is a threat at that moment due to some false information. She might then end up hurting him while trying to fend him off. Or, in a darker fanfiction, there could be an alternate universe where Hinata has turned evil and deliberately targets Naruto to cause him harm.
Perhaps in the fanfiction, Kakashi is influenced by a dark power. This power corrupts his mind and makes him turn on Naruto. It could be related to some ancient curse or a new enemy's ability that targets Kakashi's mental state. Naruto, being the target, would then be at the mercy of Kakashi's attacks, creating a lot of drama and conflict in the story.
Perhaps Sakura is in a state of extreme stress. Maybe she has a lot of pressure on her, like trying to save a village or a loved one, and Naruto's actions, which might seem reckless to her at the time, cause her to snap and hurt him without really meaning to.
Snape could be distracted by his own dark thoughts or memories. For example, if something reminded him of his past with James Potter, his hatred for Harry's father might cloud his judgment for a moment and cause him to accidentally cast a spell in Harry's direction.
It could also be due to a sense of isolation. If all his friends turned against him for some reason, perhaps being wrongly accused of a heinous crime. Naruto, who values his bonds deeply, might find such a situation unbearable and choose to end his own life.
One possible reason could be his childhood as an outcast. Growing up without parents and being shunned by some in the village made him feel like he didn't belong. This could have led to his low self - esteem. Another reason might be his struggles in school. Naruto wasn't exactly a star student at the ninja academy, and constantly being compared to his peers in a negative way could have made him think less of himself.
One possible reason could be the burden of his past. Naruto has faced a lot of hardships and the memories might be overwhelming him, making him want to be alone. For example, the loss of his master Jiraiya might have left a deep scar, and he might feel that isolating himself is the only way to deal with that pain.