One idea could be a time - travel fanfiction. Naruto Uchiha (assuming it's an AU where Naruto has Uchiha heritage) somehow travels back in time and meets Kushina Uzumaki. They could form an unexpected friendship as he tries to protect her from the events that would lead to her death. He could also use his knowledge of the future to change things in the village for the better.
Another plot twist might be that Kushina Uzumaki has a secret power that she's been hiding, and Naruto Uchiha is the only one who can help her fully unlock it. However, unlocking this power comes with a great cost that they both have to face together.
One idea could be a story where Itachi and Kushina meet in a parallel universe. In this universe, the events of the original Naruto storyline are altered, and they end up on the same side, fighting against a new common enemy. Their unique abilities, Itachi's Sharingan and Kushina's powerful chakra, would make for an interesting combination in battles.
A really unexpected plot twist could be that Kushina has some secret power that she's been hiding, and it's the only thing that can save Itachi from a certain death. But in order to use this power, she has to sacrifice something very dear to her. This would create a tense and emotional situation where both characters have to make difficult choices.
For Naruto, you could show his growth in terms of his leadership skills when he's with Naruko and Kushina. He could learn to be more patient and understanding, especially when Naruko might have a different approach to things. For Naruko, her character could be developed by showing her struggle to be recognized in a world where Naruto already has a reputation. Kushina could be developed by exploring her motherly side more deeply, as she interacts with both Naruto and Naruko.
One possible reason could be a misunderstanding. Maybe Minato thought Kushina had done something to endanger Naruto when in fact she hadn't. In the heat of the moment, he lost his temper and slapped her.
The Naruto x Kushina romance in fanfiction can be quite interesting. Fanfic writers might focus on the idea of Kushina seeing Naruto grow up and be proud of him. They could have tender moments like Kushina helping Naruto with his studies or training. There could also be a plot where they face challenges together, like protecting the village from a new threat. This kind of fanfiction allows fans to imagine a different family dynamic for Naruto that he was deprived of in the original story.
Minato might be a common character. Since he is Kushina's husband in the original story, his presence can add an interesting dynamic. Also, Jiraiya could be there. He was Naruto's mentor and his interactions with the harem situation could be quite humorous.
In a fanfiction, if Minato were to slap Kushina, it would be a huge shock to the Naruto - Kushina relationship. It could potentially cause a rift between Naruto and his father Minato in Naruto's mind. Also, Kushina would likely be deeply hurt and angry, which might lead to her distancing herself from Minato. This event could also change the way Naruto views his family's past and his parents' relationship.
Sure, there are 'Naruto x Kushina' fanfictions. A lot of them are centered around family themes. Since Naruto grew up without his mother, fanfiction writers like to imagine scenarios where he can have a closer relationship with Kushina. They might write about Kushina teaching Naruto some of her special skills or just sharing mother - son moments that Naruto always longed for.