Both MLs are comic book character who come to the real world and fall in love with the FL.
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Both FLs are cartoonists, MLs are their villains they created. Both involve crossworlds travel and the leads falling in love.

FL and ML have an age gap in both dramas, with the younger ML falling first, but the FL viewing him as a younger brother for years before finally accepting him.

One is season one, the other season two.
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Both are movies that are based upon the same story.
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Both are movies that are based upon the same story and have beautiful special effects.
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Both MLs are wealthy and important people who are injured and lose their memory. They then get rescued by the poorer FL who they've met before and end up staying for a while in her village until they regain their memory.

Both are about the poorer FL taking in the amnesiac wealthy CEO ML who has been in an accident.
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Both FLs grew up in the house of the ML until their mothers were wrongly accused of murder and driven to their deaths by the ML. Both dramas have an identical scene of the ML as a child pointing a bloody finger at the FL's mother. As an adult, the FL returns, marrying the ML to take revenge on him/his family.

Both leads work together in some entertainment field and dislike each other immediately. Neither knows that they are online confidents and friends. Both MLs find out the FLs' identity first and keep it a secret for a while.

Both FLs travel from present day to a historical world that has supposedly magical objects which are simply things from modern day, like a watch or a gun.

Both FLs are from an isolated tribe and have a position of power/leadership. Both MLs are princes who accidentally wash up in the river surrounding the FL's village and conceal their identity/motives.