Another theme is unrequited friendship. Naruto sees Sasuke as his closest friend, but Sasuke's actions sometimes make Naruto feel like that friendship is not mutual, leading to hurt feelings. It's often about Naruto's struggle to hold on to that friendship in the face of Sasuke's coldness.
Well, 'Pain of the Promise' is a fanfiction in this category. Here, Sasuke breaks a significant promise to Naruto which hurts him badly. It delves into Naruto's inner turmoil as he copes with this new reality and how it affects their relationship.
It could be that in the fanfiction, Naruto's character is developed in a way that Sakura, within the sasunaru concept, doesn't approve. For instance, if the fanfiction makes Naruto too weak or too different from his original self. Also, if the fanfiction focuses too much on certain relationships that she doesn't like, she would hate it.
In some Sasunaru fanfictions, Sakura might hurt Naruto emotionally. For example, if she chooses Sasuke over Naruto in a very cruel way, it can break Naruto's heart. She could say mean things about his dreams or his past as an orphan, which would deeply wound him.
It could mean that in the sasunaru (presumably a relationship concept within the Naruto fandom) context, the character Sakura has a dislike for Naruto fanfiction. Maybe it's because the fanfictions often deviate from the original story in ways she's not fond of.
It can create some division. Those who like Sakura might be offended by such fanfictions. But on the other hand, it also gives a platform for Sasunaru fans to express their creativity in a way that suits their ship preference.
Well, it's a rather unique and unconventional fanfiction idea. Usually, in the original Naruto series, this isn't the case, but in such a fanfic, the author might have created a whole new alternate universe or storyline to make this happen.
One reason could be to add drama. By having Naruto hurt Sakura, it creates conflict which is a key element in storytelling. It can make the plot more interesting and engaging as it forces other characters to react and deal with the situation.
On the other hand, Naruto could also be understanding. If he realizes that Sakura has her reasons, even if they are wrong, he might try to forgive her. Naruto has always been one to see the good in people, and he might hope that they can work through whatever has caused this situation. He may try to talk to her calmly to resolve the issue, showing his maturity and his belief in their friendship.
Sometimes, in fanfiction, Sakura might use her medical skills against Naruto in a negative way. For example, if she withholds treatment or gives him a wrong diagnosis out of some conflicted feelings towards him. This is quite cruel and can cause both physical and emotional harm to Naruto.