Perhaps some rogue ninja from other villages. They might see Naruto as a symbol of Konoha's power and want to take him down to weaken Konoha. These rogue ninjas could be led by a powerful and vengeful shinobi who has a grudge against Konoha. So when Naruto is alone on a mission or something, they attack, and that's when Minato steps in to save him.
Well, one possibility is that Minato arrives just in time to save Naruto from a powerful enemy like Orochimaru. He could use his Flying Raijin to quickly reach Naruto and then use his other jutsu to fend off the attacker.
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 fanfiction, Naruto and Minato often represent a connection between generations. Minato was a great ninja in his time, and Naruto is following in his footsteps. Fanfictions can explore how Naruto lives up to his father's reputation.
I'm not sure if there is such a specific fanfiction. Fanfiction can cover a wide variety of themes and scenarios, some of which might be rather strange or controversial. However, Naruto fanfiction often explores different relationships and alternate storylines, but this particular one seems a bit unorthodox and I haven't personally come across it.
One popular theme is Minato getting to know Naruto in the afterlife. Since Minato died when Naruto was a baby, fanfictions often explore their relationship in a spiritual realm.
One of the main similarities is their self - sacrifice. Minato sacrificed himself to save the village and his son. Naruto has also shown that he is willing to put himself in harm's way for the greater good. He's always the first to jump into a dangerous situation if it means protecting those he loves. Another aspect is their leadership qualities. Minato was a great leader as Hokage, and Naruto has developed into a great leader as well, inspiring those around him.
Minato would likely be extremely shocked. Naruto is his son, and the idea of Naruto attacking him would be completely unexpected. He would probably try to talk to Naruto first, to find out what is wrong and why he is being attacked.
You can try websites like Fanfiction.net or Archive of Our Own (AO3). They have a vast collection of Naruto fanfictions. Just search for 'Minato' and 'Naruto' in the search bar, and you'll get a list of relevant stories.
Minato could also teach Naruto about leadership. As the Fourth Hokage, he led Konoha. He could share his experiences on how to make tough decisions for the good of the village and its people. He might tell Naruto stories of past battles and how he strategized to win, which would help Naruto in his future as a leader in Konoha.