reika's manga / #Manhwa(1609)

Twins (the boy, a devil born from a wish, and the girl a normal human being). GL makes a wish that she won't have to marry the old man her dad chose for her to the "Devil" created by her ancestors and ends up "turning" her brother into the Devil and gets raped. From there she feels guilt and scared of her twin bro, because she thinks it was all due to her wish that he became the way he is now. In actuality, he wasn't even suppose to be born but their mother wished for a male heir and that put the Devil in her womb along with GL. (Hence the incest but not incest arguments) Things get messy as she agrees to marry the old man to separate them from each other but once again, ML comes and goes on a killing spree to save her and their relationship gets even more complicated from there on.