Joon-gi (played by Kim Tae-hoon) is So-hye's doctor. Given that So-hye is dying, that's a very awkward position to be in. While Joon-gi obviously wants So-hye to get better, So-hye's problems are just as much mental as they are physical at this point. In So-hye's general desperation to find some last minute meaning in life, she has been willing to latch onto any kind of validation possible- even if it means an obviously unethical relationship with her own physician.
It's to So-hye's credit that, when she's not horribly drunk, the woman is perfectly capable of realizing how petty her desires are. The trouble is that this always just lands her back in the same cycle. So-hye pushes people away on the assumption of shallowness, and this always ends up locking her out of any more meaningful relationship down the line. So-hye isn't a bad person so much as she is chronically at a total loss when it comes to what she actually wants out of life.
Hae-seong is a very wonderful contrast to all that. Given the slightest bit of encouragement by So-hye's impulsive kiss, Hae-seong has been obsessed ever since then with trying to get close to So-hye. Yet he also has a surprisingly good understanding of scale. Like So-hye, Hae-seong cares deeply for his loved ones and is ready to jump up at a moment's notice to help them even if it means temporarily abandoning his own interests.
Seol's character remains somewhat thinly defined as her just being the daughter-in-law to a generally terrible family. The age gap issue with her love interest Sang-wook does come up, though, and I was surprised the character age gap ended up being so relatively small compared to the fourteen year gap between Park Si-yeon and Ji Soo. This also, by implication, puts So-hye in her mid-thirties rather than her late-thirties.
While this difference may seem mild, bear in mind that So-hye isn't that upset by the bad prognosis. What really bothers So-hye is that she doesn't appear to have accomplished anything with her life to date. That's a very real personal crisis that happens to just about everyone in life, even without flashier aspects like So-hye's job factoring in. The premise of "Fantastic" is mainly just a way to force So-hye to come to terms with how she sabotages her own best chances at happiness, while we wonder if Hae-seong really is a decent enough guy to be able to overcome that resistance
Source:HanCinema
