Both FLs are modern day women who time travel to the past and enter the palace, encountering the many princes there.

Both are mini dramas in which the leads are caught in a time loop that always ends with them dying, and must figure out who's behind it to survive and get out of the loop.

Both the leads are connected in some magical way and keep dying over and over and moving slightly back in time, trying to figure out how to survive the events that caused their death the first time.

Both FLs are poor, solve cases and are medically trained in some way, MLs are wealthy and connected to the palace. Both FLs are adorable and MLs initially cold.

Both leads are raised as siblings, ML loved FL from long ago but is a little mean to her.
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Both are Korean BLs with an office setting and manager-employee relationship and similar personalities between the couples.

Both are office BL romances, with an opposites attract couple.
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Both are mini dramas in which one of the leads approached the other to take some object, but ended up genuinely falling in love. Both FLs were pregnant when they left and ML has a son he doesn't know exists. Both FLs have amnesia when they reunite with the ML.

Both have the same director so the same style. Both have demons/monsters forming relationships with humans and tragedy.

Both are dramas in which the MLs are from a comic book and the FLs are from the real world, and the two meet when one crosses over to the other's world.

Both are mini dramas in which the MLs are from a comic book and the FLs are from the real world, and the two meet when one crosses over to the other's world.

Both are dramas where one of the leads (ML vs. FL) is a manga character who comes to the real world and falls in love with the other lead who is human.