Both about detectives that fall in love with criminals they should be arresting. Except the genders are reversed.

Both have a supernatural and historical element to them. Both have a special prince who struggles to become king while fighting demons/spirits. Both have a tribe girl who helps him (who also has an older sister) and who he eventually falls for. Both also have an evil priest/shaman and some sidekicks to complete the love polygon.

The leads are similar and they both have secrets that they keep from their husbands as well as ulterior motives. There are other character parallels such as ayeula/xueyuen and zhao/shen-er as well as the Mu family matriarch and Dowager Lu.

Similar female leads - both are initially unaware of their royal lineage and work as spys/soldiers. Pre-Joseon era. Complicated love stories and political intrigue. Sisters fighting.

Set in a similar time period. Starts with parental story then moves to children after a few eps. Involves sisters and royalty. Complicated romances mixed with family secrets and political intrigue. Length.

Girl dresses as boy to study, makes a friend and eventually falls in love with him.

Complicated/sophisticated plot of a girl losing loved ones and trying to get revenge, falling in love along the way. Also epic love triangles!