It could also be related to her popularity among their peers. If his sister is more well - liked and has a lot of friends, Naruto, who has often been an outcast, might feel envious. He might wish he had the same social skills or charm that his sister has, which allows her to fit in so easily.
One possible reason could be to protect her. Maybe she has some special power that attracts dangerous enemies, and Naruto, being the strong and protective character he is, seals her power to keep her safe from those who might misuse it.
Maybe Jason is jealous because Jackson is more popular in the fanfiction world. He might get more attention, better storylines, or more fans. It could also be that Jackson has a certain charm or power in the fanfiction that Jason lacks.
It could be that his sister has some special abilities or talents that the family or the village values more. For example, if she has a very rare and powerful bloodline limit, everyone's attention would be drawn to her. In a ninja world, power and potential are highly regarded, so Naruto might be overlooked because his sister seems to have more of that 'special something' at first glance.
It could be that there was a prophecy related to his sister that made the family think she was more important. For example, a prophecy that she would be the key to saving the village in the future. And in their short - sighted view, they abandoned Naruto to focus all their resources on her.
Perhaps Sakura is jealous because of her own insecurities. She might be comparing herself to both Naruto and Ino. Naruto has his own charm and strength, and Ino has her grace and popularity. Sakura, who might be struggling with her own self - worth, could see their interactions and feel envious, thinking that they are better off without her or that they have something she doesn't.
In the fanfiction, Sakura could be jealous because she has an ego. She might have thought that Naruto would always be there waiting for her. But when he falls for Hinata, it bruises her ego. Additionally, she may have seen Naruto as her safety net, someone who would always support her no matter what. Losing that special status to Hinata makes her envious and jealous.
One reason could be jealousy. If Naruto is getting more attention or has achieved more in the ninja world, his sister might be jealous and this could lead to her actions that hurt Naruto, either by spreading false rumors or directly confronting him in a hurtful way.
It could be that she was curious about how you would look like as a girl. She might be into fashion and wanted to see if she could create a 'female version' of you using her clothes and accessories. Also, she might have been bored and thought this would be an interesting activity to pass the time.
One possible reason could be to protect her. Naruto might believe that by leaving, he can draw danger away from his sister. For example, if there are powerful enemies targeting him, he doesn't want his sister to get caught in the crossfire.
Maybe he misses Naruto a great deal. Fanfiction might offer different scenarios and stories about Naruto that he finds interesting. It could also be that he wants to see how others perceive his son in fictional tales.