In the fanfiction, it could be that a powerful enemy uses a forbidden jutsu that merges Naruto's consciousness with that of a world where Minato is female and Kushina is still alive. Naruto has to adapt to this new reality and figure out how to work with them to break the jutsu. During this time, he discovers new aspects of his parents' personalities. Female Minato might be more nurturing yet still have the strategic mind of his father, and Kushina could be even more protective. They form a strong bond as they fight to return Naruto to his own world.
One possible plot could be that Natsumi is a new character who befriends Naruto. Through Naruto, she gets to know about Kushina. They then form a unique bond where they all support each other in Naruto's journey to become Hokage. Natsumi might have some special skills that complement Naruto's and Kushina's abilities.
One idea could be that as Minato is dying, he passes on his special jutsu knowledge to Naruto in a final moment of father - son connection. Kushina, on the other hand, tries to comfort Naruto while also mourning Minato.
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.
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.
One possible plot could be that Naruto discovers a hidden jutsu that allows him to time - travel. He goes back in time and meets his mother Kushina. Meanwhile, Hinata, who has always been in love with Naruto, somehow also gets involved in this time - traveling adventure. They all have to work together to face an old threat that was once defeated by Kushina but has now resurfaced. This could lead to a lot of character development, especially for Naruto as he gets to know his mother better and Hinata gets to prove her worth to Naruto in a whole new setting.
One idea could be that the female Naruto has unique abilities that catch Minato's attention during a mission. They start to train together and gradually develop feelings for each other as they learn from one another's skills.
At first, Naruto might be really confused by the presence of a female Minato. But as they start training together, he'd see her skills and start to respect her in the same way he did his father. With Kushina, he'd feel an instant connection as his mother. As time goes on, they'd become like a family unit, with Naruto seeing female Minato as a new version of his father and having a closer relationship with Kushina than he ever did in his own time since she's alive in this fanfiction.
Perhaps in this fanfiction, Minato and Kushina leave Naruto because they are cursed. They fear that the curse will harm Naruto if they stay close. So, they go into exile. As Naruto grows up, he starts to discover clues about his parents' real reason for leaving and sets out on a quest to find them and break the curse. This could lead to many adventures and character - development moments for Naruto.
Well, one possibility could be that Naruto, with some Saiyan powers, has to protect Kushina from a new and powerful enemy. Maybe he uses his Saiyan strength and speed along with his ninja skills to keep her safe.
If Minato didn't die in the fanfiction, he could have been a great mentor to Naruto. He could have taught Naruto advanced ninjutsu much earlier, and Naruto might have become even more powerful at a younger age.