Both are lighter dramas with a FL who comes from a different world and enters the body of a girl who has died, taking over her life. ML is royal, suffers from some medical condition, and is initially antagonistic/threatening toward her, but she is the only one able to help/cure him. There is scheming within his family to replace/kill him.
Both are historical/fantasy dramas with the same actor as the ML portraying an emperor. The FL is an unfavored member of his harem who the ML dislikes at first but then slowly falls in love with her. Both dramas have magic/witchcraft, and at some point in the plot the FL ends up in another body. Both dramas have a similar tone/feel.
FL revives in the body of a different girl and must live her life including being married to the ML. The ML is cold/harsh to her at first but later genuinely falls in love with her. The SML is the brother of the ML and he loves the FL and wants the throne. Both are historical dramas with fantasy elements and a similar not too serious vibe.