They are both based on the classic French novel "The Count of Monte Cristo" even though Goodbye Mr. Black is based on the manhwa of the same title with the Count of Monte Cristo motif - revenge.
Both male leads are playboys who like to seduce and play around without any emotions attached; and they also have complicated relationships with their fathers. They also have a female "best friend" or step-sister with whom they make plans together.
The plots are almost identical - a married woman suddenly meets her ex crush and her relationship/marriage starts falling apart because she is weak.
The plots are similar because they deal with three men and a mysterious baby. Neither of them is father though, I think.
Both dramas have a theme of unconventional family, in Marmalade Boy they swap partners while in the other one they have partners of same sex.
Both are very difficult and thought-provoking movies that explore the victims of Sino-Japanese war and its consequences.
Both dramas' leads are transgender girls who want to lead normal lives. The plots revolve around them.
Another Korean erotic film that is very explicit but also beautifully shot. There's also a gay couple in it.
Women come up with a plan to take revenge on one man who has wronged them.
They are very similar in terms of how they present the bullies and the bullied.
They both revolve around bullying and how a bully can easily become the bullied.
The plots are very similar: a good girl disappears and the investigation reveals many secrets.