... so he's flirting with his sister, while his other sister is after his bones? wtf kind of plot is this. I need to know why Japan is so into incest
That we know of… there’s another story I’ve read where FL/ML were raised together because ML was a royal in hiding. It also could be possible that the situation is like Jenny said, where the brother was brought into the family for the purpose of one day marrying one of the girls.
You’re not wrong that there are a lot of manga with siblings to lover stories, but not all of them are necessarily incest.
I think it has to do something with control. A younger sibling can't run away and has to live with you from day one, a younger sibling has to tolerate physical contact with you, a younger sibling has to love you without you putting much effort into your relationship, and a younger sibling has to obey you as the older sibling. I think weird mangakas just like the idea of having a pre-made relationship without any effort from their side and a relationship the sibling can't and won't want to escape from
He really went for the "if you like it put a ring on it" approach (≧∀≦)