both are about an undercover investigator in a drug dealing industry also portraying the process of building trust between the new member (investigator) and leader of the "gang"

There are not many similarities, only the vibe, but there is no romance in the Kingdom. Both share stories of fighting the unfair government. In both, there are main leads who are fighting for justice and with monsters.

Even tho there is no parallel universe used there are some similarities :
- main lead is a police officer
- solving a murder
- a romance between ML and FL
- 2 personalities