They're suspenseful, crime-centered dramas that focus on the crime-solving process.
Both MLs are mostly emotionless men with a tragic past and ties to a serial killer.
The MLs change after getting into a relationship with a bright, stubborn female.
Both FLs have a job related to solving crimes.
Both dramas make you want to keep watching once you start.

In both, there's a marriage of convenience between a serious, older businessman and a stubborn and willful, much-younger woman. The men misunderstand the female's relationship with another close male. Both dramas also have rich families, scheming relatives, and a slow, hate-to-love romance with lots of bickering.

Both series have romance between a warm, level-headed doctor and a cool military man. There also have bandits and military missions.

Weir is the male lead and plays a gangster who bullies and eventually marries the female lead. The overly kind female lead is TSTL, and she also has an equally stupid parent who negatively affects her life. The plot is full of cliches and frustration (for the viewers) but somehow manages to have a happy ending.