Iruka could be one. He's always been like a mentor to Naruto. He might have some knowledge about Minato that he shares with Naruto. For example, he could tell Naruto about his father's kindness towards students at the ninja academy.
Jiraiya is another likely character. He was Minato's teacher. So, he could share stories about Minato's training days, like how hard Minato worked to master his skills. Jiraiya might also tell Naruto about his father's dreams and ambitions for the village.
The Third Hokage, Hiruzen Sarutobi, would be a very important character. He was around when Naruto's parents were alive. He could have hidden records or memories that he might share with Naruto. Another possibility is Jiraiya. He was Minato's teacher and Naruto's godfather. He would have a wealth of knowledge about Minato and Kushina, and he could be a key figure in helping Naruto learn about his parents.
In some fanfictions, Kakashi could also play a role. He is very knowledgeable and has seen the Rasengan in action. He might offer some tips on chakra control, which is crucial for Naruto to master the Rasengan.
Marinette might also play a role. Even though she doesn't have direct knowledge of Adrien's family at first, she is very observant. She could notice something odd about Adrien's behavior when he starts to search for his father's wish and offer her help. Together, they could piece together the mystery from different clues around the city.
In many fanfictions, it could be through finding old documents or letters. Maybe he stumbles upon a hidden scroll in his home that contains some information about his father. For example, it might be a letter from his father to his mother that gives some clues about his father's personality or his role in the village before Naruto was born.
Iruka could be a main supporting character. He has always been like a father figure to Naruto in a way. He could help Naruto process the new information about his real parents, providing emotional support and also sharing his own memories of Naruto growing up, which could contrast with the new knowledge about Minato and Kushina.
When Naruto finally realizes the sacrifices his father made for the village and for him. For example, learning that his father sealed the Nine - Tails inside him to save the village at the cost of his own life. This realization can be a very emotional moment as Naruto understands the depth of his father's love and selflessness.
Well, in many such fanfictions, Naruto might start learning his father's jutsu when he discovers some hidden scrolls or when a mentor who knew his father decides to teach him. Maybe it could be someone like Jiraiya who reveals some secrets about his father's techniques.
There could be some original Asian - inspired characters. For example, a young martial artist from a small village in China who Naruto takes under his wing. This character could be eager to learn from Naruto and would be one of the main focuses as he grows under Naruto's guidance.
Sasuke could be one of the people who help him. Despite their past differences, they have a deep bond. Sasuke has his own skills and knowledge that could be useful in Naruto's situation, like his Sharingan abilities which could help in detecting enemies while Naruto is hiding his face.
Iruka - sensei could be one of those who help Naruto. He has always been like a father figure to Naruto and would offer emotional support. Rock Lee could also be a great helper. Lee, who has trained his body to be extremely powerful, could teach Naruto some physical combat techniques that don't rely on eyesight. And of course, the Nine - Tails inside Naruto might also play a role. It could potentially share some of its power or knowledge to help Naruto deal with his new situation.