Here are Spoilers from Ch.33-43!

SPOILERS:
------------------------------------------------------------------------------------------------------------










I'm way too lazy to summarize chapter by chapter, so I'll just provide a general summary. After Kangmu called the cops at the hunting lodge, Kirin and Kangmu are under suspicion about the events of the final murder but Kangmu is under especially heavy scrutiny for all of the murders since our favorite detective has access to a certain psychologist. This psychologist has seen Kangmu multiple times as an adolescent and thus, is one of the few people who's capable of pointing the spear of suspicion exactly where it belongs. Consequently, the detective calls in a hotshot expert to shed light on the truth of the final murder. This new expert manages to figure out that Kangmu and Kirin switched shoes while staging a perilous struggle in the forest (since their story is that the recently deceased guy tried to kill Kirin by throwing him off the cliff but that Kangmu managed to rescue him in time). The expert states that it's possible to convict Kangmu but only with solid evidence as opposed to conjecture. Mr. Detective tries his damndest to convict Kangmu with solid evidence via his forensic team as well as trying to get either Kirin or Kangmu to fess up to the truth. As of now, he's unsuccessful, though he did manage to plant a few tiny doubts in both of their heads. Another reason why the detective is hellbent on convicting Kangmu is due to the fact that he wants to separate him from Kirin, as he believes that Kangmu has enticed Kirin into his sick little world.

Some additional things:
1. Kirin finds a photo of himself that he's never seen before, in addition to letters of correspondence between Kangmu and his sister. Kirin then goes to Kangmu's apartment and demands to know how Kangmu met his sister. Kangmu admits that he met Kirin's sister at a hospice shortly before he went abroad to the U.S. He was visiting some unconscious old person (there was no mention of who it was) while the sister was there as a volunteer. The sister forces some small talk onto Kangmu and it turns out that they're both medical students, although Kangmu is a year higher than her. She then goes on and on about how much of a brother-complex she has while Kangmu disinterestedly thinks of how much of a chatterbox she is. Then, he says that, since the sister shared some things about herself, he thought, whimsically, that he might as well reciprocate and idly wonders if she, too, will reject him as abnormal and look at him in the same way you would a monster, just as his mother did. As it turns out, when he was little, his mother brought home a small white dog. As he gazed at the dog, he wondered if its insides would look as pretty as its outside and thus, sliced open its stomach and pulled out its innards. His mother came upon this scene and was, of course, horrified. On the other hand, the young Kangmu looked wholly detached since he didn't feel that his actions were either abnormal or wrong. When the sister hears his childhood tale, she, contrary to Kangmu's expectations, tries to console and empathize with him.
2. The sister then asks Kangmu to exchange contact details so that she can provide what little help she might be able to, since she realized that Kangmu wanted someone he could confide in. The two then keep up a correspondence and since the sister won't shut up about Kirin, Kangmu develops an interest/curiosity in Kirin and decides to go to his university to take a candid picture of him.
Now, this action means a lot to Kangmu, since he normally only takes pictures of dead things (which he started doing as a child in order to perfectly preserve dead things without having to deal with the fuss of rotting corpses and the issue of where to store them so his parents wouldn't find out).

There's a lot more to say, but I'll stop the summary here for now. Let me know if you want more.
~~~~
Now, I know that there's much professional debate about whether psychopaths can feel empathy and the answers are mixed. So, let's not get into that and focus, instead, on this manhwa's portrayal of our resident psychopath, Kangmu. Kangmu is portrayed as a psychopath who can logically comprehend when as well as why people feel a certain way but it doesn't register emotionally with him—he has no emotional empathy. This fact is reflected when he comes across a devastated Kirin who was crying at the cremation locker of his sister (Kangmu was there because he had someone investigate what happened to the sister after he stopped receiving correspondence from her, which also proves that he cared about her. After all, she was the closest thing he had to a genuine friend, even if he didn't realize it. And besides, if he didn't care about her, he would never have bothered to investigate her status after she stopped corresponding with him, much less show up at her cremation site). Both Kangmu's facial expression as well as his thoughts are detached from the situation. Even so, he thinks, idly, about the contrast between the lively Kirin from the candid photo he took and the devastated, lifeless Kirin that lies before him. He thinks that he doesn't want Kirin to look like this--that he wants him to get back on his feet and be the way he normally is. So, he then gets to work planning everything: how to spread rumors about his little members only club, how to set up a system of surveillance cameras around all of the members' homes so that he can monitor their every move and act accordingly, etc.
~~~~
So, the verdict thus far is: yes, he genuinely cared about Kirin's sister and yes, he genuinely cares about Kirin (after all, in addition to Kirin being the only living thing that Kangmu has taken a photo of, he is also the only person that Kangmu has thrown childish temper tantrums at when he thought that Kirin was showing signs of rejecting him). Did he feel pretty good when he killed some of the club members? Yes. Was he motivated, in part, to kill the club members since he now had a "legitimate" reason to kill humans instead of animals? Yes. Does any of this detract from the fact that he does actually care about Kirin and his deceased sister? Absolutely not. We, as humans, tend to have multiple factors that dictate our behavior at any one time.