Well, it would completely turn the story upside down. The family relationships are so crucial in Naruto. If Naruto were Kushina's grandfather, it would mean a whole new set of character dynamics. For example, Minato's relationship with Naruto would be extremely different. Instead of being his father, he would be some distant relative. And Naruto's connection to the Uzumaki clan would be much more complex and ancient. It could also change how Naruto obtains his powers. Maybe he would inherit some ancient Uzumaki abilities in a different way than in the original story.
In the fanfiction, a possible backstory could be that Naruto, after achieving great power and peace in his own time, decided to use his abilities to explore the past. During this exploration, he accidentally or purposefully got involved in the lives of his ancestors. He might have fallen in love with a woman from the Uzumaki clan in the past and had children. These children then passed on their genes through generations until Kushina was born. It could also be that there was some sort of experiment by an ancient shinobi that went wrong or right (depending on how you look at it). This experiment somehow connected Naruto's future self to be Kushina's grandfather by altering the fabric of time and family relations in a very strange way.
Another aspect could be that the fanfiction delves into how Kushina's presence affects Naruto's relationships with others. For instance, his relationship with Sasuke could be different. With a strong maternal figure in his life, Naruto might be more stable emotionally and be able to approach Sasuke in a more understanding way, which could potentially change the whole dynamic of their rivalry and friendship.
He could be a powerful and respected shinobi from the Uzumaki clan. Given the Uzumaki's reputation for strong chakra and unique abilities, Naruto's grandfather might have been a key figure in the clan's history.
In Naruto fanfiction, Kushina's pregnancy can be a significant plot point. It could explore the anticipation within the Uzumaki family and the village. For example, Minato might be extra protective, and the village might be looking forward to the birth of a potential powerful shinobi. Fanfic authors might also delve into how Kushina copes with the physical and emotional changes during pregnancy, adding depth to her character.
Fanfiction often shows Kushina's influence through Naruto's values. Since Kushina was known for her strong will, Naruto might inherit that and show even more determination in tough situations. For example, when facing a powerful enemy, he might draw on that inner strength from his mother.
Well, at first, it might be a bit awkward as they adjust to being husband and wife. But as time passes, they start to understand each other on a deeper level. Kushina could help Naruto deal with his insecurities and Naruto could support Kushina in her goals for the village. They might have small arguments here and there, but overall, their love and respect for each other would grow.
Kushina's training in the fanfiction might also impact Naruto's mental state. Knowing that his mother is there to train him gives him more confidence. He feels more connected to his family and his Uzumaki heritage. This new - found confidence reflects in his battles, where he is more fearless and decisive.
At first, they would likely be a bit awkward since they've never really interacted before. But soon, the bond of mother - son would strengthen. Naruto would share his adventures with Kushina, and Kushina would listen intently, offering her own experiences as an Uzumaki. They would grow to understand and support each other deeply, with Kushina guiding Naruto in both his personal and ninja life.
They would likely develop a complex relationship. On one hand, Kushina is his sensei, so there would be a sense of respect and authority. But on the other hand, Naruto knows she is his mother in the original story, so there might be an underlying emotional bond. It could be a relationship where Naruto looks up to Kushina as a mentor but also feels a deep connection that is different from a typical student - teacher relationship.