It is quite regrettable that the show took such a long time to become this good because all the nonsensical stuff at the start must have put a lot of people off. It is unusual in Kdramaland because in most instances, it's the first half that's better than the second. These last 4 episodes have been very decent because the show has ditched a lot of the slapstick, tampered the nuttiness and taking itself far more seriously. And so it should. At its very core the show is dealing with some serious stuff. What Taesung has done and is doing to the villagers is wicked and criminal. People have died because of their wanton greed. In fact, people are still dying.
On hindsight, I really wish that they hadn't made so much of a mystery of KSH's trauma. It would probably have made him a much more relatable character from the start. His amnesia was a plot device and it didn't gel with everything else about him in a way that made sense. That said however, it is good that the drama maintained some degree of consistency with regard to his greed, his need to accumulate wealth and be the top dog, as it were. There are consequences as there should be. This puts him at odds with JYJ... which it should because she is a ethically driven, altruistic physician and her worldview clashes with his. She wants to help people and save them. His way of thinking is to mitigate a bad situation and salvage what benefits he can. Hers is to expose the corruption and stop the entire operation because there can be no middle ground in such a situation. The human cost outweighs any potential financial benefits.
I have no doubt that the show wants to present him as a kind of antihero. The materialistic corporate shark that will ultimately take down the behemoth that is Taesung. It won't be the law enforcement officials or the authorities (because most of them are up to the necks in doggy poo) but the former insider who does it all. We all know he could have blown the lid off the whole thing when JYJ was in custody but instead he chose to leverage whatever information he had to save her and to reap benefits for himself. His default position is to manoeuver and manipulate his way out of things. He isn't a good guy by any existing moral standards but he is a devious one... and he is the man for the job because he can manoeuver his way through. Using a thief to catch a thief as it were.
Redemption for KSH is in the horizon... The inner tug-of-war has already begun especially with the way JYJ has framed this dilemma. "It's me or the money." Essentially that's what it is.
So she's not appealing to him on the basis of his better self or appeal to his moral code... that probably doesn't exist at the moment. What she's certain though is that he really does actually like her a lot. So, she does what she always does, tries to save him. And she does it by appealing to his desire for her. In effect what we have is a battle... not for his soul necessarily... but a battle for love to triumph over greed. They're still working within the limits territory of self-interest but hey, it's a start.
Apparently bad guys can really fall in love. JYJ seems to believe it. I think it's possible too. KSH isn't going to transform into Mother Teresa overnight or maybe ever.
But love can slowly guide him on the right path if the one who loves can prioritize the one who is loved over all other desires.