Gangnam B-Side

Preety similar concept
ML is same for both drama and some of the supporting cast
Action, thriller, crime, mystery
Something related to Gangnam, ganster & all

Gangster world/setting.
The subplot of Dae Su & Jung Ae in AI reminded me of Gil Ho & Jae Hui in GBS.

The dorama is also about the dark side of Korea: drug use, prostitution (including teenage prostitution), sexual slavery, rape, murder, gangsters....

TV series with similar atmosphere, gang nightlife, mafia, drugs and so on! Police work! There are great actors in both series!