In the opening scene of "The Merciless", a couple of obvious criminals are having a dish of seafood, and discussing the unfortunate implications of of eating cuisine that appears to be looking at you. The end to their conversation is abrupt, and when the dust has settled, Jae-ho (played by Sul Kyung-yu) get one last ominous look at the fish, clearly the real villain. Then we see Hyeon-soo (played by Im Si-wan) exit jail and walk onto the set of a music video.
Both of these character introductions are interesting and noteworthy, and for awhile "The Merciless" continues that streak with a wild jailhouse scene where bored inmates entertain each other by playing mild restriction fight club. But after that, the more I try to remember of "The Merciless", the fuzzier the movie's actual plot becomes. It doesn't help that some of the most basic exposition is really weirdly late. We don't even find out why Hyeon-soo is in jail until maybe a third of the way through.