It could also be related to some prophecy or ancient rule in the fanfiction's world. Kushina might have been bound by a rule that stated she had to abandon Naruto to protect the greater good. This could involve things like preventing a greater disaster or fulfilling a necessary sacrifice for the village's future.
Maybe in this fanfiction, Kushina was under some sort of mind - control or false information. She might have been tricked into believing that leaving Naruto was for his own good. It could be that an enemy made her think Naruto would be safer without her around.
One possible reason could be that Kushina was forced to leave Naruto due to some external threat she thought would endanger him more if she stayed. For example, if there were powerful enemies after her and she feared they would use Naruto to get to her.
Well, it might be about Naruto growing up without Kushina's presence. Maybe he has to face challenges alone and discovers things about his mother in the process.
One possible plotline could be Naruto's struggle with abandonment issues. Since Kushina left, Naruto might have a harder time finding his place in the village. He could become more withdrawn and have to fight even harder to prove himself. Another could be the search for Kushina. Naruto might embark on a journey to find out why she left and try to bring her back.
One possible reason could be some sort of dark influence or curse that makes her lose her maternal instincts. Maybe a powerful enemy targets her and in order to protect Naruto from further danger related to her, she feels forced to abandon him. Another reason might be that she is made to believe false information about Naruto, such as that he will bring great disaster to the village in the future.
One possible reason could be a mission. In many Naruto - related stories, missions often take characters away from their families. Naruto might have received a highly important and dangerous mission that requires him to be away from Kushina for a long time.
It could also be due to some external influence. Perhaps an enemy used some kind of mind - control or manipulation on Kushina. They made her think that Naruto was a threat, so she decided to disown him. In the Naruto universe, there are many powerful villains who could potentially do this kind of thing.
Maybe she's been possessed. In some fanfictions, characters can be taken over by dark forces. So Kushina could be under the control of some evil entity and that's why she hurts Naruto.
I think Minato could also be a main character. As Naruto's father, he might play a role in Naruto's life even though Kushina is absent. He could be a guiding figure or a source of mystery for Naruto, especially if Naruto discovers things about his father in relation to his mother's absence.
It could also be related to some hidden family secrets or prophecies. Maybe there was a prophecy that Naruto would bring great destruction in the future and Kushina, believing in it, thought she had to stop him before it was too late. This would be a very complex and heart - wrenching betrayal if it was based on such a false premonition.
One possible reason could be a misunderstanding. Maybe some false information was spread about Kushina being a threat to the village, and Naruto, in his role as Hokage or a powerful figure, felt he had no choice but to banish her to protect the village. Another reason might be related to some sort of dark influence or curse that made Naruto act out of character and banish her.
One possible reason could be that Kushina has a very strong and intimidating personality. In the Naruto universe, she was known to be a tough kunoichi. Naruto, who might be used to more gentle or reserved people around him, could be scared of her boldness.