One possible reason could be that she later realizes Naruto's true nature and potential. Maybe she sees how strong and kind - hearted he is despite the hardships he faced. She might regret not being there for him during his growing - up years when he needed a mother figure.
It might show Kushina trying to make amends. She could start by reaching out to Naruto in small ways, like leaving him little gifts or messages. Naruto, at first, might be skeptical but as he sees her sincerity, they start to build a relationship.
Kushina would most likely experience deep remorse. Remorse for not being there for Naruto when he needed a mother. There could also be a sense of longing in her, longing to be part of Naruto's life and to make up for all the lost time. And of course, she might be filled with self - loathing for her past actions.
One interesting angle is how Harry's relationships at Hogwarts would change. Without the trauma of his upbringing at the Dursleys', he might be more outgoing and make friends more easily. Another angle is how the story of Voldemort's return would be affected. Harry, with the support of his parents, might be more proactive in dealing with Voldemort from the start. Also, the relationship between Harry and Dumbledore could be different. Dumbledore might not need to be as much of a guiding figure as Harry already has his parents' influence.
One reason could be the motherly love. Kushina always loved Naruto deep down. Leaving him means missing out on his growth and important moments in his life. Another reason might be realizing the hardships Naruto faced without her presence. She probably feels guilty for not being there to protect him from the loneliness and the many challenges he had to endure in the village.
Well, if Lily and James regretted disowning Harry in fanfiction, it could completely shift the whole dynamic. Harry would likely grow up with a very different mindset. Instead of being the underdog at the Dursleys', he might be trained in magic from a young age by his parents or their friends. This could make him more confident and perhaps even a bit cocky. He might also have a stronger sense of family and belonging right from the start, which could influence his relationships at Hogwarts. For example, he might be more open with his friends about his family and not feel that sense of isolation that he had in the original story.
Well, in a typical scenario for this kind of fanfic, Kushina might have left Naruto due to some difficult situation or misinformation. When she discovers Naruto has become 'godlike', perhaps with extraordinary powers and a great reputation. Her regret could lead to her attempting to reconnect with Naruto. She may face obstacles like Naruto's initial resentment or the complex political and social situations in the Naruto world that prevent a smooth reunion.
Well, it could lead to her trying to make amends. Maybe she starts to secretly protect Naruto from the shadows, which adds a layer of mystery to the story. Her regret might also cause her to interfere in Naruto's relationships, like with his friends or mentors, in an attempt to make up for her past actions.
Maybe it's because she sees Naruto's strength and how he has overcome so many difficulties despite her absence. She realizes that if she had been there, she could have made his journey easier. Also, she might regret not being able to watch Naruto grow up, miss his first steps, first words, and all those precious moments that a mother should be a part of.
The main characters would be Kushina and Naruto. Kushina, as the one who regrets her past action of abandoning Naruto. Naruto, who has become 'godlike' in the fanfic, is the center of Kushina's regret. There might also be other supporting characters from the Naruto universe like Jiraiya or Kakashi who could be involved in the story, perhaps as mentors to Naruto or as those who witness Kushina's attempts to make amends.