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.
One possible plot development could be that Minato uses the knowledge of Naruto's past to help him train better. Maybe he reveals some hidden family jutsu or techniques that Naruto can use to become even stronger.
Minato would likely be devastated. He sacrificed his life for Naruto, hoping for a great future for his son. Seeing Naruto die would shatter his hopes and dreams. He might first be in denial, unable to believe what he's seeing. Then, his grief could turn to anger, either at the situation or at those he believes are responsible. It's a tragic scenario that would change Minato's afterlife perception and his sense of purpose, which was always tied to Naruto's well - being.
The aftermath could be Minato's quest for revenge if Naruto's death was caused by someone. He would use his skills and knowledge to track down those responsible. Or, he could be plunged into a deep depression. He might isolate himself from the other spirits or entities in the afterlife. His whole existence could become centered around his grief and his memories of Naruto.
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.
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.
Well, one possibility could be that Naruto has some sort of visionary ability where he can see snippets of the future during his past adventures. For example, he might see the final battle against Kaguya while he's still on a mission with his team as a genin. This could change his approach to training and how he interacts with his friends, as he tries to prepare them for what's to come.
Madara may view Naruto as a symbol of hope in a different way. He might realize that Naruto's past, full of hardships, has shaped him into a force for good. His experiences of loneliness and then finding friendship could make Madara see that Naruto has the potential to change the ninja world in a positive way. So, instead of just seeing him as a threat to his plans, he could start to see him as an ally or at least a worthy opponent with noble intentions.
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 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.