It could be because of the way Naruto's power sometimes goes out of control. When the Nine - Tails' chakra leaks out, it can be quite intimidating. Sakura, not knowing how to handle it or being scared of it, might lash out and call Naruto a demon. Also, in the early days, Naruto was often ostracized, and Sakura may have been influenced by the general perception of Naruto as something 'other' or dangerous.
In certain fanfiction scenarios, the author might want to create drama or explore the complex relationship between Sakura and Naruto. By having Sakura call Naruto a demon, it sets up a conflict. Maybe there are misunderstandings or misinformation. For example, if there are villains spreading false rumors about Naruto being a demon - like threat, Sakura could believe them initially and use that term.
Perhaps in the fanfiction world, Naruto has other relationships or commitments that make him avoid Sakura. For example, he could have made new friends or allies who don't get along well with Sakura, so to keep the peace or not get involved in drama, he stays away from her.
In fanfiction, Naruto could hate Sakura due to her treatment of him. She often overlooked his feelings in the original series. Fanfic authors might exaggerate this aspect. For example, if Sakura continuously dismisses Naruto's achievements or makes him feel inferior, it can build up to a strong dislike or hatred in the fan - created stories. Also, some fanfictions might explore a darker side of Naruto where his pent - up emotions turn into hatred for Sakura, perhaps as a way to show his growth into a more complex character with a wider range of emotions than just the positive ones shown in the original anime.
Another reason could be that she values the authenticity of the original Naruto narrative. Fanfictions are often the product of fans' wild imaginations and might not align with the official story. She might be a purist when it comes to the Naruto story she is a part of, and thus hates fanfiction that strays too far from the original.
One possible reason could be if Sakura constantly criticizes Naruto's abilities in a very harsh way. In the story, Naruto has always been striving to prove himself, and if Sakura doesn't show any faith in him, it might make him angry.
In fanfiction, sometimes the writers have their own interpretations. They could see Naruto's character in a way where his goals and dreams, like becoming Hokage, are so all - consuming that he simply doesn't have the emotional space to care about Sakura. His attention is diverted to more important things in his mind, such as protecting the village and his friends in a more general sense rather than having a special care for Sakura.
In some narusaku fanfiction, Naruto might avoid Sakura because the story could be exploring different relationship dynamics. Maybe the author wants to create a more complex plot where Naruto has his own reasons, like he's focused on his ninja goals and doesn't want any distractions from Sakura at that moment.
In fanfiction, it could be a way to create new plotlines. By having Naruto stay away from Sakura, new conflicts and story arcs can be introduced. For example, it might lead to a situation where Sakura has to re - evaluate her own feelings and actions towards Naruto, or it could create a rift between them that other characters have to help bridge in the story. Also, some writers may simply not be interested in the typical Naruto - Sakura relationship and choose this as a way to deviate from the norm.
It could be that in the context of the fanfiction, there is a lot of tension. Naruto might be in a hurry or in a very serious situation, and Sakura's chatter is getting in the way. For example, if they are in the middle of a battle plan or facing an immediate threat, Naruto needs everyone to be focused, and Sakura's talking is a distraction, so he tells her to shut up.
Well, in fanfic, the writer can take creative liberties. It could be that Naruto has grown and evolved in a different way than in the original story. He might have seen Sakura's flaws more clearly over time. For example, her obsession with Sasuke could be seen as a negative trait that affects the team dynamic. And as Naruto values the team highly, this could cause him to develop a dislike and eventually hate for Sakura.
Well, it could be that in this fanfiction, Naruto has some sort of hidden agenda. He might call Sakura ugly as a form of reverse psychology. He could be thinking that by doing so, she'll prove him wrong and become more confident. Or perhaps there's some miscommunication or misunderstanding between them. For example, Naruto misheard someone talking about Sakura in a negative way regarding her looks and he wrongly believes it, so he says she's ugly.