Dowun died by stabbing himself in the heart. In the final act, he sacrificed himself so that he can save the mc in a way. His death made him as an escapegoat. Someone that people could blame for whatever chaos that happened in their Kingdom. He stabbed himself in front of MC afaik and fre falled to the fire. Unfortunately, he never confessed his feelings. Until the end, he kept that truth. Maybe it's his way of unburdening the MC with any more complicated feelings and for her to just move on with life without the possible baggage that his confession might bring. Afterall, he left her as the Leader of the empire and leaders should not bother themselves with these types of emotions especially since the Kingdom, after he left needs an undistracted leader. (My personal theory)

Notice how we didn't get some sort of POV from dowun? All of them are complex characters. I see how people villainized Dowun way too much, but yeah it's in the structure and a lowkey biased way coz we only get Lyon's POV. I will never continue this again(I know the ending already though), I've been in an angst streak, I cannot anymore lmao