Responses
This is very close to my own theory, because I like Soowon from the start as a complicated and many layered character. Plus all the small details that tell us about his real persona and not just seeing a polite and approachable mask of his (っ°Д °;)っ
I think a new theory has come to play. You know that soowon has been leaving the castle and roaming the villages ever since he was little right? That's where the corruption starts, he sees all of what king Il has done to the kingdom. Killing his father was just the icing on the cake, and not only revenge, but he wants to rebuild the kingdom as a strong one because he knew that king Il and his only daughter yona would not be able to save it.
Soowon has been sickly and weak his entire life. He has a terminal illness. That's why he had to rush to the throne and take over. The easiest and fastest way was to kill king Il and sacrifice yona and Haks friendship. And by eliminating the king, he would have majority control of all of the kingdoms assets, thus the plot so far.
That's also why he asks zeno about his immortality, he does not want it, but he wants to continue living, now that he has the acknowledgement that Hak and yona are still alive and kicking.
And even if he does die, he now knows that Yona is fit to be queen now. Which is another reason why Hak defected to the sky army, and yona decides to stay in the palace.
Oh my god
A bucketful of info dump. I need to calm down. This is just a theory, but it makes so much sense
（/TДT)/