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.

Both are heavy subjects in which the FL endures something horrible and the ML tries to protect her, ending up in prison.

Both MLs go to prison after injuring in revenge someone who hurt/killed someone they love, reuniting with the FL years later.

Both MLs are "killed" in a car accident and then wake up in the body of their brother, becoming involved with the FL again who was their lover and now believes they're dead.

Both are historical mini dramas with a love/hate relationship between the leads, with the FL out for revenge and believing the ML betrayed her in the past.

Both are short length dramas in which a couple breaks up, only to reunite years later at which point the ML discovers he has a young daughter. Both MLs have a disapproving mother who tries to force them apart.