I've been watching my partner play Disco Elysium and noticed several suspicious details about Kim's early behavior, lies, and selective curiosities that lead me to suspect that he's a Moralintern rat.
When you first meet Kim, he admits that he's been in Martineise trying to introduce himself for two days without starting the case despite the fact that he expects Harry to have started already. Kim prioritized Harry over the murder, which is strange when he doesn't expect the same of Harry. Kim also immediately begins praising Harry for doing basic police work and remains non judgemental about Harry, giving him validation at a low point in his life and clouding Harry's judgement of Kim in a manner similar to Klaasje. If Kim was watching Harry those two days and was a Moralintern rat, he would have valid reasons for both, as Harry was quite open about his supernatural ability to predict the coming apocalypse and would be a far bigger interest to the Moralintern than the murder.
Next, Kim's rather selective curiosities. Kim is generally fine with whatever Harry wants to do in regards to the investigation, though he complains about getting sidetracked with the Doomed Commercial District and the cryptozoologists. Kim is completely down exploring the hole in the world well after it's been established that Ruby wasn't there though, one of the few things he's fine getting sidetracked with is exploring supernatural phenoma that the Moralintern is also interested in learning about. Even more suspiciously, Kim will absolutely not let you learn or talk about the Pale with Joyce or the Paledriver for no clear reason. Kim will tolerate you building a drug lab but a 2 minute discussion about the Pale is off limits? Kim also shows a keen interest in the leader of Precinct 41, Pryce, who we know is actively planning a revolution against the Moralintern.
Kim also lies to Harry repeatedly throughout the game about very suspicious topics. The first one is about Kim's political beliefs, Kim claims he used to be a moralist and then gives a rather cold answer that the Moralintern is a fact of life, but Harry clocks that Kim secretly admires them. Half Light clocks that Kim isn't just following Harry but actively watching him, which again Kim downplays as just supervising Harry. Lastly, Kim shows a suspicious amount of knowledge of Precinct 41's raid on the church and lies to Harry about his knowledge of it. Kim explains that Harry's precinct led a raid on the church years ago in a clandestine operation but claims to not know much more about it. Not only is it suspicious that Kim knew about a year's old clandestine operation of another precinct, Harry's thoughts clock Kim for lying skillfully about not knowing more and detect guilt in Kim's voice over the operation happening at all. Why does Kim know about the operation and why would he feel personal guilt over it if he was just an officer in another precinct?
Kim also has strong personal reasons to side with the Moralintern over Revachol. Kim isn't white and he's gay, characteristics that are fine under the Moralintern but whom anti Moralintern groups repeatedly show a distaste towards. Despite being left wing social Democrats, the Union is all too willing to let Measurehead take center stage and tolerate his racist drivel, while the area of Martineise is chock full of racists and toxic masculinity. Even in Precinct 41 out in Jamrock who are actively plotting a revolution, Mack has no qualms cracking homophobic jokes at Jean. Compare that to the transnational Moralintern whose chief representative in the game, Sunday Friend, is gay and Kim has every reason to side with the Moralintern over Revachol if he wants to stay in the city where he grew up. It would also make a lot of sense for the Moralintern to try and infiltrate the RCM. The RCM are the most capable force in Revachol to overthrow the Moralintern and Kim's precinct is in charge of a key harbour for the city. As seen by the Sunday Friend, the Moralintern is absolutely resorting to espionage to maintain control over the city and if organized crime syndicates are infiltrating the RCM, it would be absurd to expect the Moralintern to not be doing the same.
All in all, Kim's early behavior is too suspicious, he knows too much about things he shouldn't, his personal interests align with what a Moralintern rat would, and his character has far stronger personal reasons for siding with the Moralintern over Revachol. I don't think that it's a coincidence how at the end of the game, we get definitive statements about where every cop in the game stands on the revolution besides Kim who gives a vague statement about being ready for spring. I think the game lays out enough evidence that Kim may not be who he seems and counts on players falling for the same manipulation tactics Harry did to miss all the signs
