Minato would likely have a more reserved reaction, but his eyes would shine with pride at Naruto's achievements. He might be seen smiling softly when Naruto masters a difficult jutsu. Kushina would be more vocal. She would shout words of encouragement even though Naruto can't hear her. When Naruto shows his Uzumaki tenacity, Kushina would be beaming with pride, and she would probably nudge Minato and say something like 'Look at our boy!'
Minato would probably be very proud. He might notice Naruto's use of his own jutsu and be impressed by how Naruto has developed his skills. Kushina would be more emotional, maybe crying at the sight of Naruto growing up so well.
One popular one might be where they watch Naruto's training sessions in a sort of time - warp scenario. It shows their reactions to his growth and determination.
On a more personal level, they could face internal guilt. As Naruto grows up and achieves great things on his own despite their neglect, Minato and Kushina may realize what they've missed out on. This realization could cause them a great deal of internal turmoil and regret for not being there for their son when he needed them.
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.
At first, Naruto and Kushina might start to distance themselves from Minato. They could avoid him and not talk to him as much. As time goes on, the hatred might grow deeper. Naruto could start to oppose Minato in public or in important village matters. Kushina might also try to influence others in the village against Minato.
Some fanfictions might revolve around alternate universes where Minato and Kushina have different fates. Maybe in one, they are both more powerful than in the original story and change the entire landscape of the ninja world. These stories often offer unique takes on their characters and the Naruto universe as a whole.
One interesting fanfiction could be about Minato and Kushina's relationship before Naruto was born. It might explore how they fell in love and their hopes for the future. Another could be a story where Naruto discovers some hidden secrets about his parents through some magical or mysterious means. Maybe a time - travel fanfiction where Naruto goes back in time and gets to meet his parents when they were young.
There's a fanfic called 'Minato's Return'. In this story, Minato somehow returns and gets to see Naruto's growth. It's really interesting to see how he interacts with Kushina, who is also there in the story, and how they both guide Naruto in new ways. The descriptions of their family bond are heartwarming.
In many Naruto fanfictions where Naruto meets Kushina and Minato, it often creates a very emotional scenario. Naruto finally gets to meet his parents who he has only heard about. It could be a heart - warming reunion where they share stories, hugs, and Minato and Kushina get to see how far Naruto has come.
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.
It might be due to jealousy. If Minato was getting more attention or praise in the village for his achievements while Kushina felt overlooked, that could create resentment. Say, Minato was constantly being hailed as a hero for his speed and battle tactics, and Kushina, who also had great power, felt like she was in his shadow.