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.
Well, one possible tattoo design could be the Uzumaki clan symbol. It would represent Naruto's connection to his family heritage. Since he grew up without his parents, having this tattoo could be a way of carrying their legacy with him. Another could be a tattoo of his Nine - Tails form. It might symbolize his power and how he has tamed the beast within. And a third option could be a tattoo of his friends' symbols combined, like Sasuke's Sharingan and Sakura's forehead protector mark, to show his bond with them.
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.
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.
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 possible storyline could be that Naruto gets tattoos and piercings as a sign of his growth and independence. He might use them to show his newfound confidence and to distinguish himself from his previous self. For example, he could get a tattoo of the Nine - Tails on his arm to symbolize his connection with the powerful beast inside him.
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 meaning could be a sign of his individuality. In the world of fanfiction, Peter might use tattoos to set himself apart from the normal, expected image of Spider - Man. It could also represent a new phase in his life, perhaps a more rebellious or self - discovery phase.
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.