Perhaps there is an event where Naruto's team blames him for a failed mission, even though it wasn't his fault. This could make him resent them.
It could be that in the fanfic, Team 7 starts to act in a way that goes against Naruto's moral code. For example, if they start using cruel or unethical methods to achieve their goals. Naruto, being the character he is, would not stand for such behavior and this could lead to his hatred. Additionally, if there is a personal loss that Naruto experiences which he blames on Team 7, that would also contribute to his negative feelings.
One possible reason could be a misunderstanding. Maybe his team made a decision without consulting him, which made him feel left out and thus led to hatred. For example, if they took on a mission without him, Naruto, who values being part of the team, might feel betrayed.
One possible reason could be that Naruto's dad was not around during his childhood. In the Naruto story, Naruto grew up alone and ostracized, and he might feel that his dad abandoned him, which could lead to hatred in a 'dark Naruto' scenario.
Well, it could be a combination of things. Maybe he saw through some hidden agendas of the village elders or was constantly overlooked for important missions despite his skills. Maybe there were trust issues with his teammates or mentors that built up over time and caused this hatred.
One possible reason could be that he feels neglected. Maybe his family was always too busy with other things and didn't give him enough attention. This lack of attention during his formative years could have led to feelings of resentment.
Perhaps in this fanfiction, Naruto has been influenced by some external force. It could be a dark entity that has corrupted his view of Team 7. He might see them as a hindrance to achieving some greater, more self - centered objective. Also, it could be that Naruto has had some sort of personal revelation about his past and blames Team 7, or certain members of it, for things that he now believes held him back in the past.
In a fanfic, if Naruto is left behind by his team, he might first feel a sense of abandonment. He could then use this as motivation to train harder on his own. For example, he might discover new jutsu or ways to improve his skills. He could also cross paths with other characters who help him grow in different ways, like an old hermit who teaches him some unique wisdom.
Well, it could be that Naruto has been betrayed too many times. Maybe he discovers that some of his closest friends have been using him all along for their own gains. So he starts to hate everyone, and the story could be about his journey of isolation and self - discovery as he tries to come to terms with his new feelings.
Maybe in the fanfic, his sisters got some special powers or attention that Naruto felt was unfair. So he started to hate them out of envy.
It could be due to a misunderstanding. Perhaps there was an incident where his sister was involved, but Naruto misinterpreted her actions as something malicious against him. Like she might have accidentally broken something precious of his and he thought it was on purpose.