One quick thought about ep 16 of CH
The fact that YS is the President's son explains something that bugged me before so much - why did Undaddy wait so long for revenge? He himself admitted to flunkie that he was capable of clearing the dead men's name years ago and we see he's pretty good in the revenge business in general.
Before it was always weird why he wanted YS to do the bulk of the work and why he did his best to train him to kill and why he was so mad that no matter what YS was no killer and would refuse to kill the Five no matter what. I always wondered WTF was with Undaddy's displeasure when he could so easily kill them instead of YS' revenge or in tandem with it (i.e. YS ruins them, Undaddy kills them).
But now it all makes sense - of course he is only implementing his plan now - he wanted YS to be old/trained enough to do it because that way the irony of the Five being brought down by a child of one of them - what could be a more perfect revenge? And he wanted YS to kill the Five with his own hands (going as far as blackmail him, manipulate him, emotionally torture him in every way, threaten him and attempt to kill those he loves) because that would ultimately mean that Yoon Sung would unknowingly kill his own father (who was, significantly, left for the last, so as to 'groom' YS into a soulless murderer slowly) thus leading to the most perfect, diabolical revenge ever (clearly Undaddy took President's betrayal the hardest. The rest were anonymous politicians, he was their commander who swore to bring them home).
And that would also explain not only why he took YS (he needed him as a tool for revenge; why should President's child live well when his father killed Undaddy's friends; he's freeing Kyung Hee from demonspawn; every time Undaddy would look at YS' face he'd see his enemy - that quote makes so much more sense now) but why he treated him so horribly from day one, inflicting endless physical, mental and emotional abuse on him and now doing his best to wreck any chance of happiness he has. I know I was not the only one wondering how nuts was Undaddy to treat the son of his savior like an animal. Yeah. But he's the son of his enemy, so it all makes perfect sense. (FWIW, I do think Undaddy has grown somewhat fond of YS, despite his will, but certainly not enough to derail his vengeance or expect him to live through it).
And that would also explain why Undaddy tries to drill into Yoon Sung's head that he has no future. Because he doesn't. How is Yoon Sung going to get out of it all/escape alive after (1) he ruins/gets revenge on the freaking sitting President of Korea (there is a reason Undaddy hasn't let YS know who the final target is) (2) is there any doubt that part of Undaddy's revenge on the Pres would be gloating to him that he was brought down (and if Undaddy had his way, killed) by his own son? I am pretty sure this is when YS would find out the truth and is there any doubt that it would destroy him, mind and soul, utterly? He's already teetering on the edge as is.
So yeah, what kind of future can YS have after bringing down the President who is his own father. None.
Ohhh, Undaddy, you are the devil. I am even forced to reluctantly admire you. From a safe distance away - like half a planet.