Probably his time at the Ninja Academy. Naruto was always getting into trouble there, but it was also where he made some of his first friends. Also, his encounters with the Third Hokage could be shown. The Third Hokage was like a grandfather figure to Naruto, and their interactions were important in Naruto's development.
Definitely the story of how he met Jiraiya. Jiraiya was Naruto's mentor and teacher. Their journey together, from training in the wild to learning new jutsus, was crucial for Naruto. Also, the times when Naruto was on missions with his team, like Team 7 with Sasuke and Sakura, would be shown. These missions were full of challenges and helped Naruto become the ninja he is in Boruto's time.
Boruto might be in awe. He has always known his father as the Hokage, a powerful and respected figure. Seeing Naruto's past full of struggles, loneliness, and determination would make him realize how far his father has come. It could also make Boruto more empathetic towards Naruto and perhaps inspire him to be more like his father in some ways.
One key event could be Naruto's lonely childhood. Growing up without parents, constantly being shunned by the villagers. Madara might see how Naruto coped with that, like when he sat alone on the swing. Another could be his encounter with Iruka, who was the first to really recognize Naruto as a person, not just the container of the Nine - Tails. This moment might be significant as it was a turning point in Naruto's self - acceptance.
One key event could be Naruto's time at the Ninja Academy. He was often alone and had no one to practice with, yet he still persevered. Boruto would see how Naruto's determination started early. Another event might be when Naruto fought against Haku and Zabuza. It was a dangerous battle that showed Naruto's courage. And of course, Naruto's training with Jiraiya would be important. Jiraiya taught Naruto so much, and Boruto would understand how this mentorship shaped Naruto into the person he became.
He might be shocked. Naruto has seen a lot in his life, but seeing something new and unexpected in his son's eye could still catch him off guard.
Well, first of all, Minato would likely be shocked. Naruto's past was full of hardships and loneliness. Minato would probably experience a mix of emotions. He might be sad that Naruto had to endure so much pain. He could also be proud of how Naruto overcame all those difficulties and still managed to grow into a strong and kind - hearted person. He might even try to find ways to comfort Naruto in this fanfiction world, like giving him some long - lost family memories or advice that could have made his journey easier.
Well, Boruto could be very inspired. Naruto's past is full of struggles, from not having parents around to being constantly underestimated. When Boruto discovers this in the fanfiction, he might realize that his own problems are not as big as he thought. He could be motivated to work harder and not take for granted the things he has, seeing how much Naruto had to fight for everything.
Obviously, Naruto himself is a crucial character. His experiences and growth form the backbone of the story.
One interesting plotline could be exploring Naruto's early days of training with Jiraiya in more detail. Maybe showing his struggles and how he overcame them during that time.
It could also be that Naruto sees in Boruto's eye a sign of an emerging danger. The eye might hold a clue to a new enemy or a brewing conflict. Naruto, being the experienced ninja he is, would then start to take precautions and train Boruto more intensively to face whatever this sign in his eye indicates.
Boruto could have visions or dreams that show him Naruto's past. Maybe he enters a forbidden realm or unlocks a secret power that allows him to experience his dad's history.