Both are mini dramas with rival assassins who marry each other, with each unaware of the other's secret identity.

Both are mini dramas with rival assassins who fall in love and marry each other, each unaware of the other's secret life.

Both are historical dramas in which the FLs have their faces exchanged with another woman. Both MLs are generals and first met the FL when she had her original face.

Both are historical dramas in which the FLs are betrayed, seemingly killed, and have their faces changed by a man who finds them injured and saves them.

Both are historical mini dramas in which the FL swaps faces with another woman and returns for revenge against those who wronged her.

Both are historical mini dramas in which the FL swaps faces with another woman.
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Both FLs are seemingly killed but have their faces/identities swapped with another woman who has a brother.

Both FLs are wronged, seemingly killed in a fire, get their faces swapped with another woman, and become part of that woman's family, assuming her identity. They then continue their quest for justice under that identity with the help of the ML who is a military man.

Both are historical dramas that have a powerful queen pushing her son(s) to the throne, scheming by people in the people, and an heir to the throne who grew up outside the palace unaware of his identity as a child.

Both are historical dramas in which the ML is a prince who ends up on the run outside the palace, and helped by the FL who is unaware of his identity. Both MLs have a half brother who palace people are scheming to put on the throne in his place.

Both FLs are the daughter of a man wrongfully accused and executed, and both assume a false identity and become swept up into some pretense regarding gender (marriage to a girl pretending to be a boy vs. attending school disguised as a boy).

They're sort of a gender flipped version of each other - one of the leads (ML vs. FL) has a strange curse/illness that makes them react to something and the other lead fixes them by letting them drink their blood.