I'm not sure specifically which fanfic this refers to. There could be various interpretations. Maybe it's a very dark and emotional take where Minato, Naruto's father, is somehow in a situation to witness Naruto's death, perhaps in an alternate universe where things go horribly wrong and the normal protection Naruto has is stripped away.
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.
If Minato didn't die in the fanfiction, he could have been a great mentor to Naruto. He could have taught Naruto advanced ninjutsu much earlier, and Naruto might have become even more powerful at a younger age.
Perhaps there was a curse or a disease that he couldn't overcome. In some fanfictions, they like to introduce unique and deadly diseases that not even the best medical ninja can cure. It could also be due to a failed mission where he was caught in a trap that was impossible to escape from, leading to his death.
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.
I'm afraid I'm not aware of any particular fanfic with this exact premise that I could recommend. However, when you search on fanfic platforms, read the reviews and summaries carefully. Some fanfics might have a similar concept but not the exact same title. Maybe look for ones that explore alternate universes or dark timelines in the Naruto world.
Well, it would probably shatter their relationship. They'd be filled with grief and guilt. Minato might blame himself for not being there to protect Naruto, and Kushina would be heartbroken. Their bond would be strained as they deal with this overwhelming loss, perhaps even leading to some estrangement as they struggle to cope in their own ways.
I'm not sure specifically as there could be many novels with 'Minato' in the title. It could be about a character named Minato, or it could be set in a place called Minato. Without more context, it's hard to say.
I don't know the specific name of the Minato manga off the top of my head. It could be related to a particular genre or have some distinctive features that might help identify it.