One way it could happen is if Naruto somehow gains the ability to travel back in time. Maybe through a powerful jutsu or a unique kekkei genkai. He could then use his knowledge of future events and his combat skills to save his parents from their tragic fate.
Another possibility is that Naruto discovers a hidden power within himself that is connected to his parents. This power could give him the strength and the means to go back in time. Once there, he would use his strategic mind and his strong bonds with his friends (which he has developed in his own time) to rally support and resources to save Minato and Kushina. He could also use his experience of dealing with the Nine - Tails to prevent it from going on a rampage and causing their deaths.
Well, Naruto could save Kushina from the Kyuubi in fanfiction through his strong willpower. We know Naruto has an unbreakable spirit. He might be able to communicate with the Kyuubi in a different way, like showing the Kyuubi a future where it doesn't have to be so violent. And by doing this, he could convince the Kyuubi to release Kushina. Also, Naruto might have received some special power or training that enables him to counter the Kyuubi's attack and save Kushina.
One possibility is that Naruto has an out - of - body experience and is able to communicate with his parents in a spiritual realm. They could give him advice on how to deal with his enemies and his inner demons.
A great fanfiction concept could be that Minato and Kushina are resurrected during a crucial battle in Naruto's life. Their presence gives Naruto a huge morale boost. They fight side by side with Naruto against a powerful foe. After the battle, they decide to stay in the village and help Naruto rebuild and strengthen it. This would not only be a great action - packed story but also a heartwarming family reunion story.
The village of Konoha would also be affected. With Minato still alive, he could continue to lead the village and make different decisions. This might change the relationships between Konoha and other villages. For example, there could be more peaceful alliances as Minato is known for his diplomatic skills. Also, Kushina being alive would mean that the Uzumaki clan might have a stronger presence in the village, which could lead to new jutsu developments and a different power balance within Konoha.
One possibility is that Minato and Kushina would be overjoyed to see Naruto again. They would probably first have a very emotional reunion, hugging him tightly. Then, Minato could start training Naruto more intensively, passing on some of his most advanced jutsu techniques that he didn't have time to teach before. Kushina, on the other hand, would likely focus on the more motherly aspects. She might cook all of Naruto's favorite meals and give him the love and care he missed during his childhood. Also, their presence could change the political situation in the Hidden Leaf Village as Minato was a respected Hokage. Their return could boost the morale of the villagers and make the village even stronger in the face of threats.
In such a fanfiction, Naruto would probably be overjoyed. He could finally have a proper conversation with his parents. Minato might share some of his jutsu secrets or stories about being Hokage. Kushina would surely embrace Naruto tightly and tell him how much she loves him. They could also have a family meal together, a simple yet precious moment that Naruto has always longed for.
Perhaps Naruto would become more in - touch with his Uzumaki heritage. With Kushina being an Uzumaki, she could pass on some unique knowledge or abilities to him. He might also start to explore the history of the Uzumaki clan more deeply, which could open up new storylines and alliances within the Naruto universe.
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.
Maybe they enlist the help of other powerful ninjas. For instance, they could ask Tsunade for medical support in case Naruto is injured. They could also get intel from Shikamaru, who is known for his intelligence. By gathering a team of reliable and strong ninjas, they increase their chances of getting Naruto back successfully.
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.