Well, it could be that Sasuke has a personal goal that she believes is more achievable if she is perceived as a male. For example, she might want to rise to a high position in the ninja hierarchy, and historically, it has been more difficult for women to reach the top in that world. Also, she may be trying to fit in with a certain group or ideology that is more male - dominated. By hiding her being a girl, she can more easily blend in and pursue her dreams without the hindrance of gender - based discrimination.
Perhaps Naruto has a big dream, like becoming Hokage. She might think that in a world where male leadership is more common, hiding her gender would increase her chances of being taken seriously. People might be more likely to believe in a male's ability to lead rather than a girl's, so she hides it to pursue her goal more effectively.
One possible reason could be his deep connection with Naruto in the original story. Fanfiction might offer new and different perspectives on their relationship, which intrigues him. Maybe he wants to see how others interpret their bond, whether it's their friendship or the complex rivalry. Another reason could be that fanfiction allows him to exist in scenarios that didn't happen in the official storyline, giving him a chance to explore different aspects of his character and his interactions with other characters.
He might hide it because he doesn't fully understand his own fascination. Harry has always been on the side of good, but perhaps there are elements of the dark side that seem alluring in a strange way. He could be afraid that exploring these feelings would lead him down a dangerous path, so he keeps it a secret.
Maybe Naruto was trying to protect Sasuke from a certain danger. There could be a curse or a powerful enemy that targets male shinobi. So, Naruto uses a risky jutsu to transform Sasuke into a girl to keep him safe. Or it could be that Naruto found a strange ancient scroll with a transformation technique that he thought was something else and when he used it on Sasuke, it turned him into a girl.
One possible reason could be that Naruto is hiding his face to conceal his emotions. In SasuNaru fanfiction, their relationship is often complex and full of unspoken feelings. Naruto might be afraid that Sasuke will read his true feelings if he shows his face. For example, if Naruto has developed deeper romantic feelings for Sasuke, he may not be ready to expose them, so he hides his face as a form of self - protection.
One possible reason could be Naruto's internal conflict. In yaoi fanfiction, the relationship is often complex. Naruto might be running away because he's confused about his feelings for Sasuke. He may not be ready to face the intensity of the relationship that the yaoi concept implies.
One possible reason could be his deep concern for Naruto. Despite their complex relationship, Sasuke might be worried about Naruto's well - being after all they've been through. He could be silently guarding him while he sleeps, a sign of his unspoken affection and protectiveness.
Another reason might be related to their different ideologies within the ANBU. Naruto may have believed in a more collaborative and friendly approach within the organization, while Sasuke might have been more focused on individual achievement and power. This fundamental difference could lead to Naruto hating Sasuke in the fanfiction.
One possible reason could be to protect Hinata. Maybe Sasuke has unknowingly made a move or decision that Naruto perceives as a threat to Hinata, so he scares Sasuke to make him back off.
Perhaps they just want to enjoy the early days of their marriage without the scrutiny of the outside world. They want to have a normal relationship for a while, just the two of them. They can learn about each other in a more private and intimate setting. It's like a honeymoon phase that they don't want to be interrupted by the media or public opinions.