Nagisa's best friend might be really surprised at first. But then, being a true friend, would support Nagisa through this strange change. They would probably help Nagisa with things like choosing girl - appropriate clothes or dealing with any mean comments from other students.
He might be angry at first. Naruto has grown up alone and had to fight for acceptance. So when his parents say they regret abandoning him, he could lash out, saying it's too late. After all, he has already faced so much without them.
Kayano would be completely devastated. Since she had a special bond with Nagisa, she might become withdrawn and filled with rage, vowing to take revenge on whoever was responsible.
Their other classmates like Okuda would be very sweet. She might make them some special potions or concoctions as wedding gifts, something that symbolizes good luck and a long - lasting marriage. And she would be all shy and cute about presenting it to them.
The son could ask for some time and space if he feels too overwhelmed in the moment. Then, when he's ready, he can sit down with his parents and have a proper conversation. He can also share some educational resources about homosexuality with his parents to help them understand better.
In some fanfictions, Naruto may become extremely bitter. He could feel a deep sense of betrayal and this might fuel his determination to become stronger, not for the sake of the village at first, but more for self - vindication. He might isolate himself from others and struggle with his identity.
I recommend "The Peasant Daughter-in-law". The female protagonist of this book also raised a child alone, while the male protagonist was the eldest young master of a peasant family. The plot also involved the situation where the female lead avoided certain people in order to protect her child. The entire novel was set in business and farming, telling the story of how the female protagonist started her own career and found true love. I hope you like my recommendation, Mwah~
One possible reason could be that Naruto has some sort of power within him that they fear. Maybe it's a power that they don't understand and think could be dangerous, so they hate him out of fear.
In some versions of the fanfic, Harry might have a sort of instinctive understanding that his parents had a good reason for leaving him there. So, while he's still not happy about it, he might be a bit more accepting. Maybe he can sense some sort of protection spell around the Dursleys' house that gives him a small sense of security.
Lily would probably be very warm and welcoming. She was known for her kindness. She might immediately take a liking to Ginny, seeing her as a strong - willed and intelligent young witch, much like herself. James, on the other hand, might be a bit more boisterous in his welcome. He could be impressed by Ginny's skills in Quidditch, if that comes up in the meeting, and would likely be glad that Harry has found such a remarkable girl.