Perhaps it has to do with a new and mysterious disease. In fanfiction, new and unique diseases can be created. This disease could be something that attacks his unique chakra system, which is different from others. Since his body is so reliant on chakra, if the disease disrupts it enough, it could lead to his death.
Well, it could be for creative exploration. Maybe the writer wants to see how Naruto would turn out if he had a difficult family situation like being abused by his mother. This could then lead to a different path for his relationship with Hinata. It might also be a form of catharsis for the writer, expressing some darker emotions or ideas through this fictional and extreme scenario. Additionally, it could be an attempt to analyze the impact of a negative family environment on Naruto's development in the context of the Naruto - Hinata relationship.
It could be due to Sakura's feelings for Sasuke. If she's overly focused on Sasuke and Naruto gets in the way of her plans regarding Sasuke in some way, she might lash out and hurt Naruto without really meaning to cause serious harm.
One possible reason could be to protect Hinata. Maybe Sasuke has unknowingly made a move or decision that Naruto perceives as a threat to Hinata, so he scares Sasuke to make him back off.
One possible reason could be a vampire attack gone wrong. Maybe a rogue vampire targeted Bella and inflicted a near - fatal wound. Another reason might be related to some sort of dark magic or a curse that was unknowingly placed on her. It could also be due to a self - sacrifice situation where she put herself in harm's way to save someone she loves, like Edward or one of her friends.
Well, Naruto could hate Sakura and Sasuke because in the NaruHina fanfiction context, Sakura might represent the past and all the times Naruto felt rejected by her. She always had eyes for Sasuke. And Sasuke, his actions were often self - centered and caused Naruto a great deal of distress. Naruto, as he falls for Hinata, starts to realize that Hinata is always there for him. Unlike Sakura, who is always pining for Sasuke. So, Naruto's feelings towards Sakura and Sasuke change to dislike as his relationship with Hinata blossoms.
Hinata would likely go to great lengths to save Naruto. She might seek help from the most powerful medical ninjas in the village or even venture out to find a rare herb or a mysterious healer. She would be in a state of shock at first, but then her love for Naruto would drive her to take action.
Some fanfictions might explore the idea of Naruto being betrayed by someone close to him. This betrayal could lead to a situation where he is caught off - guard and killed. It adds a dark and dramatic twist to the story.
One possible reason could be that the Kyuubi's power goes out of control completely. Since Naruto has the Kyuubi inside him, if he fails to maintain the balance, the Kyuubi's raw and unrestrained power might end up killing him.
One possible reason could be a powerful curse placed on him. Maybe an enemy with dark magic managed to put a slow - acting curse that is gradually sapping his life force.
It could be due to some kind of self - sacrifice he made in a previous battle. For example, he might have used a very dangerous spell that had a side - effect of slowly killing him to save his friends or the wizarding world.