Both involve one of the leads caught in a time loop trying to change events and save the life of the other lead who has died in their present.

Both involve the FL time traveling to the past and trying to change events to prevent the death of the ML.

Both involve one of the leads traveling repeatedly between past and present to change what happened and save the other lead, all while unravelling the mystery surrounding their death.

Both jump between past and present as one of the leads in the present tries to change the past of their high school years and prevent the death of the other lead.

Both are historical dramas in which the ML is a human who is in charge of hunting down demons/another people of which the FL secretly is. Despite this, the two fall in love.

Both are a gender flipped version of the other about an arranged marriage in which one of the leads loves the other instantly and the other is cold and takes time to fall in love. One of the leads is a demon, and the other human. Both couples, once they fall in love, are deeply devoted and inseparable. Both dramas are historical and have a similar feel.

Both FLs swap places with their sister in an arranged marriage, resulting in them meeting and falling in love with the ML.

Both FLs swap places with the SFL in an arranged marriage, resulting in them meeting and falling in love with the ML.

Both FLs swap places with the SFL in an arranged marriage, resulting in them meeting and falling in love with the ML.

Both FLs swap places with the SFL in an arranged marriage, resulting in them meeting and falling in love with the ML.

Both couples break up and the FL doesn't tell the ML she's pregnant. Years later, the two reunite, with the ML learning he has a young son. Both MLs have a chronic health condition that their child has inherited.

Both MLs are chronically ill. Both FLs become pregnant by the ML, then end up trapped in the palace by the emperor who is obsessively in love with them.