Hi, I read the book a while back but the details are a little fuzzy now. I haven't started this season yet so I can't really provide any insight to what may happen next because I don't know what they've covered. It's also important to note that the book is in chronological while the drama is obviously not, which I think makes it a bit confusing at times.
I want to provide a little insight into Noa because he's a character that can easily be misunderstood. Noa was deeply affected about finding out his real father was Koh Hansu as he had always looked up to Isak (his adoptive father). Isak was a find upstanding citizen, unlike Hansu who is involved with the yakuza. He later disappears and pretends to be Japanese, but his issues aren't with his Korean identity (that Solomon's issues). When Sunja locates him after several years, he kills himself.
As for Hansu, he stays involved in Sunja's life I think because he has feelings for her. Whether it's guilt or love, I don't know. I don't remember if he dies or not, but if he does it's towards the end of the book.
Anyway, I'm gonna have to binge watch season 2 soon so I can see what they changed.