Second Lieutenant Breda went from being the most obscure member of Team Roy to get quite a bit of spotlight -- at least just as much as any other of its components, or even more so. That's how I see it anyway. Breda didn't serve at the Ishval War either, nor we know at what exact point of his life he came in contact with Roy.

We do know that Breda was friends with Havoc time before they both met Roy. Was Havoc the one recruited before? Was it Breda? Was any of the two a decisive element in Roy's decision to choose the other one? We could really use a flashback here.

Breda is an excellent shougi player. Shougi being a chess-like board game, described in the FMA world as "played by the Eastern Island countries". Although not said explicitly in the manga, it's assumed that Breda is also a good chess player, since he's shown playing against Roy in a certain color illustration. All these facts suggest that, despite appearances, Breda is a highly intelligent individual -- which is probably one of the reasons Roy took an interest in him.

Roy, of course, asks him to go to Central with him. But not only that, he also seems to take Breda's opinion in high consideration, as we could see when the Ross incident took place. He relied on Breda the duty, not only to get the components needed to make a faux human body, but also to escort Ross to Xerxes. And something far more relevant:

     

Breda: That's good. I won't have to use this fella, then. In the unlikely event that Second Lieutenant Ross were the culprit, I had orders from the Colonel to kill her after getting whatever information from her.

This is the moment we began to see just how much trust Roy and Breda rely in one another. Roy entrusted him the most difficult of duties and Breda complied without a second thought. It was Roy's order to kill Ross in the event that she turned out to be Hughes' killer and Breda would have done it. He would have killed for Roy just because he told him to. I bet anything he would also die for him.

However, as with the rest of the Roy-tachi, Breda is not a mindless soldier who's following Roy blindly. He'd do anything for him and he will go to any extent just to help him obtain his goal, but all of this is based on the absolute faith that somehow Roy manages to bring out of everyone. He's not following his superior's orders, he's following Roy's, a man in which he trusts completely and whose ideals and dreams he can relate to.