Why are you so rude unprovoked ? I am begging ? If you don't wanna explain you are free to do so ??? I don't wanna read a 100+ chap story if it has incest in it . So if there's a logical explanation behind it which I can accept I will read it otherwise I won't that's why I asked . It's simple as that . What's wrong with knowing spoilers beforehand?
I'll do it for you, its just a summary
(I haven't read the story for a long time and I was planning to re-read it - for the people who read it already feel free to correct me)
I really suggest/encourage you to read it, my summary won't do the story any justice since to be able to fully understand the story, you have to really read it through.Every explanation is in different chapters and later chapters too (ex. chapter 1 explanation of FL crying scene is in the last few chapters of the story). The story managed to tell how FL and ML in a unique way from the present problems, past issues and how they ended up confronting the curse. (did I feel gross when I first saw the story and there was no season 2? of course i did. anyways sorry for the long rant)
long story short the "devil" after a lot of rebirths finally managed to 'attain' the FL's twin look due to their mother's wish to continue the bloodline of the duke. The main reason why the main couple is considered incest is due to the fact the 2000(?) years ago FL would do everything for her twin even if it hurts her while being in a confusing relationship with Idris (Devil). Idris watched how FL would clean, kiss and stab the preserved corpse of the twin. Eventually Idris died after FL pushed him in a dried well and thats where the curse started, The devil's love for the FL made them reincarnate multiple times just so he could finally be with FL.
On the current timeline, FL and ML have hallucinations of their past making their relationship rocky until they found out more about themselves.
there's still a factor of incest btw, the younger brother's of FL and ML. there's a glimpse in the story that he was the child of FL's maid, he was in that relationship with her.

Before i read this I am confused. How are they twins and not blood related at the same time ??? Comments are saying it's not incest but HOW . Somebody explain