Finally a historical-setting manga that actually mentioned the harm of marriage between close relatives. Istg most JP mangas that have cousins married to each other always gloss it over, and a lot of people with fetishes are okay with that.
@Eclat123 Maybe it's because Japan permits first cousin marriages. Their inbred rate was also quite high compared to other countries, based on a research from 2010. Rather than a fetish, they seem to see incest/consanguineous marriage as a normal thing? Japanese people with more non-traditional view would see this differently though.