The struggle between gods and demons is the root cause; the focus on bloodline is the lead; love and dislike are the root cause.
Failure to love is the result.
Her: Bah! You are the devil! Your whole family is a demon!
He: You are the only one in my family who is a demon, and you are still a half-hearted demon.
Her: ... Then that's why you don't want me? Or do you mean you don't love me at all?
Him: Then why have you never come to see me in ninety thousand years? Why did you wait for me for ten years but refused to wait for the moment when I finally woke up? And why did you never tell me about your many injuries?
Her: ... I... I don't know!
Him [laughing]: Then I don't know either.
PS: The main drama is a bit sadistic, but it's not so sad that it kills people, and it's a little sweet, so it's not too boring.