Hwaryun is the male lead, but we see the story from Suu's perspective. The plot is centered around these two characters primarily with Sahara acting more as a support character (for now). While Sahara does have a key role in the story, the outcome of all the decisions being made up until now is not in his hands if that makes sense. Hwaryun and Suu have a greater contribution to how this story ends versus Sahara. Sahara is just there for the ride because that was the author's intentions from the very beginning.
If you want to know why I think this way, then just think about it logically for a second: who determines whether the dragon lives or dies? Who is going to bring rain upon Rahan, ultimately? It's not Sahara. While Sahara is a major component for the bringing rain, it is actually the king that summons the dragon and performs the ritual; it is the king who decides whether or not there will be rain for his country. This story isn't about Sahara deciding whether or not he wants to bring rain to Rahan. This story is about the journey in which Hwaryun brings rain to Rahan with the help of Suu and the dragon. Suu's presence further complicates things and spices things up, which is why he can be considered to be a male lead as well. In other words, Suu's decision making is the reason for how we got to this far into the story (along with Hwaryun).
I just started reading this. I was wondering who was the ml?