V.I.P. (2017)

A beautiful killer who has everything planned out until a miss step.
VIP is a killer and police relationship and Hello monster is a killer/family relationship.

A beautiful killer uses the system to hide in plain sight.
VIP has the international aspect where GapDong small town based.

There is a crazy psychopathic male lead in both and they suffer from similar fates at the end of the series/movie.

These movies are similar in their graphic and gory nature. They equally have good fight scenes and both have an amazing plot but aren't close enough that it seems they copied each other. They both leave you to decide if it's Revenge or Justice.

similar---
psychopath
brutal murders
tenacious and loyal detectives
political power play
eye candy as psychos

Both have similar vibes though the stories are very different.
Crime , action , murder, and so on.
In a way both are about psychopath killers.