Kim Joo-hwan definitely has a workable formula. In previous and much better movies like Midnight Runners and The Divine Fury, he presents a pair of likeable guys (rookie cops in one; demon chasers in the other) who decide to join forces in order to seek justice (legal or celestial, as the case may be) then end up becoming best friends forever in the process. Why doesn't it work this time around? Once again, he's got a naive protagonist (Kim Woo-bin) knee-deep in a endless fight for the good. Once again, he's got a truly evil villain this time, a serial child molester (a hulking Lee Hyun-geol) devoid of remorse. There's even a charismatic mentor (Kim Seong-gyoon)...for the good guy, not the bad.
What Kim doesn't have is any characters with nuance. Or particularly thrilling fight sequences. Or a female character with a purpose. Or a compelling back story. Or a sense of someone growing as a person over the course of the film. Not with the hero. Not with his gamer sidekicks. Not with his dad. The biggest change we witness in Officer Black Belt is the young martial artist's decision to go from being a punky bleach-blonde to a raven brunette. That his beautician must do double-duty as the movie's almost-rape victim and the hero's stand-in auntie will give you an idea of how contrived it all feels. Officer Black Belt, you're looking tired.