I don't know who the author of Minato Novel is. There are so many novels out there and without more information, it's impossible to determine the author.
Kushina could be an important character even though she's dead in the original story. In this fanfic, her spirit or memories could play a role in Naruto's upbringing. For example, Minato could tell Naruto stories about Kushina's feisty personality and her love for the village.
Sakura could be another main character. She might be shocked by Naruto's arrest and start her own investigation. Maybe she teams up with Sasuke, who also has his own complex feelings towards Naruto. Their combined efforts could play an important role in uncovering the truth.
Sakura could be a significant character. In the context of Naruto being Minato's son, her relationship with Naruto might change. She could be more in awe of him at first or have different expectations. Also, Sasuke is likely to be a main character. His rivalry with Naruto could take on new dimensions as Naruto has the added legacy of being Minato's son. Their battles and interactions might be more intense and influenced by Naruto's heritage.
There could be Sasuke. Since Sasuke is Naruto's rival and often involved in the same major story arcs, he might play an important role in this fanfiction. His sharingan abilities could interact with Naruto's newfound speed in some interesting ways, either as an ally or an obstacle depending on the plot.
Since it's called the'minato kid story', the main character might be the kid from Minato. There could also be supporting characters like the kid's parents, friends, or a teacher. Maybe there's an old wise person in the neighborhood who gives the kid advice and also plays an important role in the story.
Rin could also be an important character. She could be the one who takes care of baby Naruto's day - to - day needs, like feeding and cleaning. She could also have a special bond with Naruto, perhaps seeing him as a symbol of hope for the future of the village.
Jiraiya is likely to be a popular character. He was Minato's teacher and has a strong influence on Naruto as well. In a time travel fanfiction, he could provide a lot of wisdom and help in the different situations they encounter. Also, Tsunade could be important. Her leadership skills and medical ninjutsu could be very useful when they are in the past, and she has her own history with both Minato and Naruto's family.
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.
The 9 - tailed fox itself can be considered a main character in a way. It has its own personality and motives within the fanfiction. It might not be a traditional character but it has a huge impact on the story. And then there could be an antagonist, perhaps someone who wants to steal the power of the 9 - tailed fox from Minato, which would make that person a key character as well.