If in a Sasuke fanfic, one possible reason could be unrequited love. If Sakura feels that Sasuke will never return her love and she has exhausted all hope, she might sink into despair. Another reason could be if she feels she has failed Sasuke in some way, like not being able to protect him or help him in his goals. Maybe she blames herself for his continued pain or suffering and sees no way out but to end her own life.
Well, in a Sasuke - centered fanfic, Sakura might kill herself if she is constantly rejected by Sasuke. Imagine she has been trying for years to get close to him, to be a part of his life, but he keeps pushing her away. This continuous rejection could break her spirit. Also, if there is some sort of misunderstanding. For example, she might think Sasuke blames her for something that she didn't do, and she can't bear the thought of him hating her, so she takes her own life. Additionally, if she is in a situation where she feels she has lost everything related to Sasuke, like his trust, his friendship, or any chance of a future with him, she might consider suicide as an escape.
One reason could be to create shock value. By having two main characters kill another important character, it grabs the reader's attention. Another could be to explore a very dark and alternate version of the Naruto universe. Maybe the writer wants to show how far characters could be pushed in extreme situations.
One reason could be if Sasuke was somehow possessed by a powerful and evil force during the Chunin Exams. Naruto might see no other way to stop this threat and be forced to kill Sasuke to protect the village and others. Another possibility is a huge misunderstanding. For example, if Sasuke was framed for a crime he didn't commit and Naruto was misled into believing he was a danger.
It could be because of a dark power corrupting Sasuke. Maybe an ancient evil force takes over him and makes him see Sakura as an enemy. In some fanfics, this kind of external influence can completely change a character's actions. Also, it might be related to Sasuke's pursuit of power. If he believes Sakura is standing in the way of his ultimate power - seeking goal, he could be driven to kill her.
One possible reason could be Sasuke's focus on his revenge. His thirst for vengeance against Itachi might make him blind to Sakura's feelings and neglect her as he is constantly preoccupied with getting stronger to achieve his goal of revenge.
Maybe to explore different character arcs. The writer might want to see how Sakura would develop as a character if she strayed from her loyalty to Sasuke. It could also be a way to introduce new characters or relationships into the Naruto fanfic world.
Well, for one, self - mutilation is a heavy and dark topic that has no place in a fictional world that is mainly aimed at entertainment and promoting positive values like those in Naruto. It would also be inappropriate because it would distort the characters of Sakura and Sasuke. Sakura is a strong - willed character, and Sasuke has his own journey of redemption and growth. This kind of plot would undermine all of that. Moreover, it could have a negative impact on younger fans who look up to these characters.
Some writers might want to explore different character traits. They may think that Sasuke has a more complex personality that could lead him to make such a mistake. Also, it could be a way to show Sakura's reaction in a difficult situation and how she might grow or change because of it. In addition, it might be an attempt to break the traditional 'happy ending' mold of their relationship in the original story.
Perhaps in the fanfic, Sasuke was being pushed to his limits. He was so intent on protecting the village from a powerful threat that he didn't realize Sakura was in a dangerous position. His Sharingan might have malfunctioned in some way, causing him to misinterpret Sakura's movements as hostile. Or, there could be a situation where an enemy was using Sakura as a shield, and Sasuke's attempt to strike the enemy ended up harming Sakura instead, all in a split - second decision.
Perhaps they leave because they feel restricted in the village. They want to explore the world and grow as ninjas outside the boundaries and rules of the village. They might also want to learn from different ninja cultures and techniques that are not available in their own village.
Maybe in the fanfic, Sasuke has some personality traits that become more difficult for Sakura to handle over time. For example, his brooding nature might start to feel like emotional unavailability rather than just his usual self. This could lead to her regret.