Recommendations

FL enters a different world and unexpectedly falls in love with the villain.
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Both have a real world FL entering a fictional world and finding love with the ML who is the antagonist of the story.

Both are short length dramas with a person from the real world entering a fictional world and an antagonist ML.

Both are short dramas in which the FL is in a fictional story (tv drama vs. story) and falls in love with the plot's villain.

Both are short dramas in which the FL is in a fictional story (tv drama vs. manga) and falls in love with the plot's villain.

Both are short length dramas with a ML who is a manga character and a FL who is from the real world. The two meet when one crosses over into the other's world.

Both are short length dramas with love story between a manga character and a person from the real world.

Both are short length dramas where the main couple are a person from the real world and a manga character.

Both dramas are set within the world of a manga with a heroine trying to change the story.
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In both, the FL is from the real world and enters a manga, falling in love with a character in the story. Eventually, the ML leaves the comics and enters the real world.

Both are short length dramas set in the world of a comics, with a villain ML and a FL who attempts to change the story to her advantage.

Aya Ruk is similar to Nang Tard because the story is around a noble having several wifes : the first one is loyal, the second/third is bad and the third one is a slave who was sold to the first wife and whom the main actor falls in love with and nominates her as his latest wife.
1) Same misunderstanding from the main actor who thought the slave's brother was her lover so he beated her very badly as a punishment and set her to be slave again.
2) Same story when the first wife and the slave became pregnant at the same time and the first wife's baby died at the birth so she took the slave's baby as her child.
3) The second wife is pregnant from a lover and died at the end of the drama.
4) The misunderstanding is solved at the end of the drama and the slave came back to be the noble's wife.

Both feature mermen as ML and takes place in a fantasy world.

Both FL are righteous and rather stoic.

Mystery, Thriller, married couple and a child… I don’t know why exactly but Flower of Evil reminds me of Kairos in a way. There’s one similarity I can think about but I don’t want to spoil it.