Ryuuji's parents are members of some sort of Society that hunts for 'Lost Precious' -- magical artifacts. Ryuuji has the makings of a great Breaker, but he dislikes the hunting part -- his parents are never home because of it. But then one day his cousin Reiko turns up and she shanghais him into assisting her with stealing a Lost Precious during a transaction. This Lost Precious turns out to be a girl, a Red Dragon! They call her Rose, and she seems to know Ryuuji. When they take her in to the Society to be examined, a Black Dragon called Onyx turns up who claims Rose is his fiancee.
And so the series starts. The series comprises of relatively short arcs, where Ryuuji has to help out some pretty damsel in distress, and they join the steadily growing group of girls who like him. Of course, Ryuuji remains blissfully unaware of this happening (or chooses to be so). He is the typical romantic action hero: always trying to protect everyone and always doing the right thing.
And that's exactly what the series is: typical. It has no spark of originality, no situations that you haven't seen a dozen times before. Sure, it looks OK and the voice acting has some big names on the roster, but that doesn't save the series from being completely dime-a-dozen mediocrity. I won't go into the details either, because there's no real point to it. That's not to say that the series is bad -- it isn't! But it's nothing special either.
So I'll give it a 6.5.