I think it makes more sense to view Gwi-ma as something internal to the characters rather than some mind controlling entity imposing some external force.
Gwi-ma, as the interior voice of shame, can only voice the shame that already exists within someone. During times of emotional crisis (ie Mira and Zoey) or when someone has done something that they ought to be ashamed of (say, ommitting certain facts about an event leading to them gaining a benefit they might not otherwise have), his voice gets much louder.
But he can't actually make anyone *do* anything.
Yeah, if Gwi-Ma can control you directly, he can make you abandon your friends or your duty to the world, can make you betray the first person in centuries to believe there was something good still in you, can make you make every single bad decision.
And it isn't your fault, if he controls you. You didn't have a choice.
And if you didn't have a choice, then what do you have to be ashamed of?
So while it may be a comforting lie for Jinu to tell himself that Gwi-Ma controls people, it's probably more accurate for Gwi-Ma to be talking to them, suggesting courses of action or giving justifications for giving in to your worst, most selfish, shameful impulses.
And when you do give in, the shame from that moment will haunt you forever. You could have chosen differently, after all, but you were weak and selfish, and you deserve everything that happened to you.
And it becomes a little harder not to listen next time
I do tend to see it that way, but I also tend to see it as some One Ring At The Cracks Of Doom shit. He can only suggest to you whatever your worst self may already have been inclined to do, but as a fully internal voice of shame, he (or the him inside your head, anyway; it’s probably narratively useful to limit the degree to which Bonfire On A Plinth Gwi-Ma can receive perfect information about other people’s internal states) knows the exact arguments that you can’t counter. At his most powerful, no one can resist him.
It’s why Rumi at the end of the movie (I keep coming back to this) could only beat him after agreeing to all his arguments and then dismissing their relevance rather than their accuracy.



















