That synopsis was really poorly written (says the small dragon is a mystery, which just reeks of trying to force a cliffhanger into a synopsis - also poorly done as it is obvious who it is), wonder which publisher released this manga.
Other than that, it's problematic that the dragon emperor seems to actually be a lolicon. The synopsis failed to describe it properly, but him saying that about her seemed to not actually be his real thoughts and only something done to fool the fbi.
At least it explains why his fated partner wasn't a dragon, and instead was a race of eternal youth. Anything else would quickly exit his strike-zone.