In fanfiction, Naruto may have nightmares because of the unresolved issues within himself. He has always strived to be recognized and accepted, and despite achieving a lot, there could still be that little voice in his head that doubts himself. Also, the prophecy about him might be a source of stress. Knowing that he has a great destiny to fulfill can be overwhelming. He might dream about failing in his mission or not being able to live up to the expectations. All these internal and external factors combined can lead to him having nightmares.
One possible reason could be the trauma he has faced in his life. For example, the loss of his parents at a young age and the constant feeling of being an outcast in the village. These past experiences might resurface in his dreams as nightmares. Another reason could be the pressure he feels as he grows older, like the weight of his responsibilities as a ninja and his role in protecting the village. Also, the fear of losing his friends, who have become like family to him, might haunt him in his sleep.
A possible reason could be for self - expression. Naruto is a very expressive character, and tattoos could be another way for him to show who he is. It could also be a way to distinguish himself from other ninjas.
It could be a genetic quirk that was dormant before. In the fanfiction, the author might be exploring a different aspect of the Uzumaki genetics where Naruto inherits his mother's hair later in life for some reason. It could be related to his growth or a new power awakening.
One reason is that the characters' personalities don't really lend themselves to such a plot. Hinata is deeply in love with Naruto and has been for a long time. Naruto also has strong feelings for Hinata. Their relationship is based on mutual respect and admiration.
One reason could be the extreme pressure of being Hokage. He has so many responsibilities, like protecting the village from external threats and managing internal affairs. It might all become too much for him to handle, leading to a breakdown.
In some fanfictions, it could be related to a curse or a dark magic spell. There could be a hidden plot where an ancient curse is placed on Naruto, and as part of its manifestation, a hole appears in his chest, which could lead to all sorts of consequences for his health and his ability to use chakra.
The main reasons are related to character enhancement. Abs can make Naruto look more heroic and powerful. In fanfiction, writers might want to show that he has reached a new level of physical prowess. Also, in some cases, it's just for the sake of conforming to modern ideals of a 'hot' male character. Since Naruto is a popular character, writers may add abs to attract more readers who are interested in that kind of physical appearance for their favorite characters.
One possible reason could be some sort of dark curse or forbidden jutsu. Maybe Naruto was the victim of a malicious experiment that altered his blood composition. Another reason might be related to his connection with a dark entity. For example, if he has some link to an ancient evil, it could manifest in his blood turning black.
One possible reason is that the fanfiction writer wants to stay true to the original essence of the characters. In the original books, their relationship was mainly about friendship, mutual growth, and shared adventures. So, the writer may not want to deviate from that and add sexual elements.
Perhaps in the fanfiction, Hermione discovers some dark secrets about the wizarding world or her own family. This new knowledge could be so shocking and difficult to process that it causes her to have a breakdown. It could be something related to the history of magic that goes against everything she thought she knew, or a revelation about her parents that throws her into emotional turmoil.
One reason could be that some fans are very purist about the original Naruto story. They might feel that fanfiction often distorts the characters or the plot in ways that go against the essence of what Naruto is all about. For example, changing a character's personality completely to fit a romantic or dark and edgy narrative that doesn't align with the source material.