One reason could be for self - protection. In a dangerous or hostile environment within the fanfiction world, hiding gender can keep Sakura safe from potential threats.
Maybe it's for the purpose of achieving a certain goal. For instance, if there's a competition or a mission that is restricted to a particular gender, Sakura might hide her gender to participate. This can add a layer of intrigue and conflict to the story as she has to keep her true identity a secret while trying to succeed in the task.
She might want to prove herself in a male - dominated ninja world. If she shows herself as female, she could face discrimination or be underestimated. So, hiding her gender gives her a chance to be seen as an equal to male ninjas.
One reason could be jealousy. If in the fanfic, Sakura gets closer to someone else Naruto cares about, like Sasuke in a different way than he expected, it might make him hate her. For example, if Sakura teams up with Sasuke against Naruto's wishes in the fan - created plot.
Protectiveness. Sasuke has seen a lot of danger in his life. He knows Sakura is a valuable person, both as a friend and as someone he cares about. So his possessiveness could stem from his desire to keep her out of harm's way. He doesn't want any bad guys to get near her.
Maybe she wants to experience the story from a male perspective. In fanfiction, different genders often have different roles and experiences. By pretending to be male, Sakura can explore how male characters are written, how they interact with others, and what kind of emotions and challenges they face.
She might be crying out of frustration. For example, if she's been trying really hard to achieve a certain goal in the fanfiction, like mastering a new jutsu in a Naruto - themed fanfiction, but keeps failing. The stress and disappointment could lead to tears.
In some fanfictions, it could be due to unrequited love. If Naruto has deep feelings for Sakura but she continuously rejects him in a cruel or thoughtless way, Naruto might feel angry enough to seek revenge. For example, she could publicly humiliate him for his feelings, which would hurt Naruto deeply and lead to thoughts of revenge. Another reason could be a misunderstanding. Suppose Sakura is misjudged by Naruto as having done something terrible when in fact she was innocent. But Naruto, in his ignorance, decides to take revenge. This can create a lot of drama and conflict in the fanfiction.
One reason could be fear. Maybe Harry discovers something about Dumbledore in the fanfiction that makes him scared, like a hidden agenda. Another reason might be to protect Dumbledore. Harry could think that by hiding from him, he is keeping Dumbledore away from some sort of danger that is related to Harry himself. Also, it could be due to a misunderstanding. Harry might misinterpret something Dumbledore does or says, and as a result, decides to hide from him.
Perhaps he sees her as a threat. Sakura is a skilled kunoichi, and Madara may want to prevent her from interfering in his plans. So he restrains her to keep her out of the way.
One possible reason could be that she sacrifices herself to save Naruto from a powerful enemy. In the heat of battle, she might put herself in harm's way to ensure Naruto's survival.
One reason could be that Sasuke realizes his true feelings for Karin were always there. Maybe in the fanfiction, he had some sort of epiphany that his connection with Sakura was more of a convenience or misunderstanding, while his bond with Karin was deeper on an emotional level.