Maybe in the fanfiction, there is a powerful enemy who wants to use Naruto's connection to his parents against him. So, they somehow manage to bring Minato and Kushina back to the physical world. When they meet Naruto, it's an emotional moment. They form a plan to defeat the enemy together. Minato uses his strategic skills, Kushina her strength, and Naruto his own unique abilities learned over the years.
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.
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.
Well, in some fanfictions, the moment when Minato sacrifices himself to save the village while Kushina is already dead is extremely emotional. It shows his selflessness and also the love he has for the village and his family. Also, the flashbacks in some stories about their early days together, like when they trained together as young ninjas and slowly fell in love, are really sweet and emotional.
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.
A possible setting could be near the river in Konoha. The sun is setting, casting a warm orange glow over the water. Minato and Kushina are sitting on the grassy bank, talking about their dreams for the future. Minato might reach over and tuck a strand of Kushina's hair behind her ear, and then they lean in and share their first kiss as the gentle sound of the flowing water provides a peaceful backdrop.
No. In the Naruto series, Minato and Kushina have a loving relationship. A fanfiction depicting abuse goes against the essence of their characters and is inappropriate.
A fanfiction could explore the backstories of these characters more deeply. For instance, how Mikoto came to be so proficient with her sharingan, and how her friendship with Minato and Kushina developed over time. This could add a lot of depth to the existing Naruto lore.
One possible fanfiction could involve Minato, Kushina, and Mikoto working together on a mission. Maybe they have to protect the village from a powerful enemy. Minato's speed, Kushina's chakra chains, and Mikoto's sharingan skills could combine in interesting ways during battles.
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.