Official English Translation on Futekiya 5u4b4q
Upon his return from battle and a strange encounter with a monster-like man, The Captain is notified by his twin brother, The King, that their Guardian Deity no longer wants to protect the kingdom. To convince the Guardian Deity to change its mind, The Captain ventures out to its mountain lair and returns with the Guardian Deity's only condition to continue protecting the kingdom: The Captain must become his mate.
Official Korean Release:
Peanutoon, Ridibooks, Bomtoon, Kakao, Naver Series, Bookcube, Mrblue
1 Volume (Complete)

Enjoyable to read, lovely art, good characters. The lack of sex (well, at least the conventional sort...) worked in this story's favor, because we get more time to flesh out both the commander and the dragon beyond the relationship i.e. the dragon's view of humans, and the commander's sense of duty and love for his country and subordinates. The two of them steal the show, of course, but even side characters aren't left as simple background decor, and their actions influence the story; the emperor was given some depth and you could feel the brotherly bond between him and the commander.
The only downside is that this really, really would've benefited from at least another volume—not because it's rushed or lacking (the ending is satisfying), but because I would've loved to see more moments between everyone. It's one of those stories that got me interested in the world beyond the couple, and how they could interact with it more.
At first you'd think the dragon is kinda jerkish but honestly he's just a child that is curious about love and companionship.