How should we deal with a sex with nephew story if we encounter it in a book?
First of all, we need to be aware that this is not a normal or acceptable relationship. If it is part of a book, we can analyze the author's intention. Maybe the author is trying to show a dark or immoral side of society. But still, we should firmly oppose any form of promotion or glorification of incestuous relationships within the story. We can also discuss it with others to make sure we have a correct understanding of the ethical implications.
If we come across such a story in a book, we should approach it with caution. Consider the context in which it is presented. If it is used as a cautionary tale to show the consequences of immoral behavior, that's one thing. But if it seems to be normalizing or romanticizing the relationship, then it is a problem. We can choose to stop reading the book if we feel uncomfortable with such content. Additionally, we can engage in discussions with book clubs or friends about why such content is inappropriate and how it reflects on our values as a society.