In fanfiction, Naruto might be jealous because he thinks that Kiba has something he doesn't when it comes to Hinata. For example, Kiba could be more confident around Hinata, while Naruto is still a bit shy about his feelings for her. This contrast could fuel Naruto's jealousy.
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 for the sake of creating drama. Fanfic writers often like to explore extreme scenarios that deviate from the original story to generate intense emotions and reactions from readers.
Perhaps it's because in the main Naruto storyline, Hinata has so many unspoken feelings for Naruto. Fanfiction gives her a platform to express those feelings more openly and in various scenarios that she may not get in the official story.
A misunderstanding is also likely. Maybe Kiba overhears a conversation that he misinterprets. For instance, he might think Hinata is talking badly about him when in fact she is just discussing a general ninja problem. This could make him angry enough to hurt her, either with words or actions.
In such a fanfiction, Hinata might be jealous of Sakura because Sakura could be more popular or confident. Maybe Sakura has skills that Hinata wishes she had, like better combat skills or more outspokenness. Also, if there's a love interest involved, and the guy seems to pay more attention to Sakura, it would make Hinata jealous.
In the fanfiction, Naruto might start distancing himself from Hinata and Kiba. He could focus more on his training to distract himself from the jealousy.
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.
One possible scenario in this fanfiction could be that Sakura realizes her long - hidden feelings for Naruto when she sees Hinata getting closer to him. She might start to act out in small ways, like being a bit more snippy with Hinata during team meetings or training sessions. However, she also has to deal with her own sense of pride and the fact that she once rejected Naruto.
Perhaps in the story, there is a competition for a rare ninja item or a special mission opportunity. Kiba, being very competitive, sees Hinata as a threat. He tries to intimidate her by making fun of her skills in a very mean way. Hinata, who is already a bit shy and self - conscious, is deeply hurt by Kiba's actions. Naruto, on the other hand, witnesses this and stands up for Hinata, which then starts a whole new plot development in the fanfiction.
One reason could be envy. Maybe Naruto sees Hinata as having something he doesn't, like a more stable family situation, and he lashes out in jealousy. Another reason might be that he's just being a typical, rambunctious kid who doesn't realize the impact of his words or actions on Hinata.