[Bisis]

It is a manhwa that consist in four volumes. I have to say I'm in the process of understanding the whole story(first for my language limits and second because I have not a real knowledge of Asian beliefs) and maybe I will have to re-read the story countless times in the future.(not kidding). And saying all that stuff, I can say that the feeling of reading that manhwa was really of taking concience of a lot of realities.

Theme of Fever can be very confusing. There are some phrases from Buddhism throughout the plot. In Buddhism, you abandon your mortal desires to reach higher status of mind and tranquility.
Fever brutally shoots against that. But it does not mean this manhwa is anti-Buddhism. Although it's not clear in the beginning, there appears to be many protagonists. Pretty much every character you see in this manhwa is a protagonist. (This includes secondary characters.)

The whole point of this manhwa is said so right at the end of its plot. Hence, until you get there, everything's pretty vague.
The plot is quite unpredictable as well. It is best just to read through until the end where you will be given purpose of protagonists.

Source: Janimes