User blog comment:B214/Question and Answers 6/@comment-99.235.66.221-20161130072057/@comment-26821288-20161214153914

Yeah, I always thought that Ddraig and Albion aren't simply polar opposites in their basic abilities (Boost vs Divide), but rather they themselves, their fighting style, their powers, their personalities, their very existances maybe, were exact polar opposites, Ddraig being a hot headed Dragon who always rushes off before everyone and just destroys everything in his way, and Albion being the calm and focused Dragon who plans things out and waits for the right timing always to use some dirty trick or sneaky move/ability. And I think that, indeed, that may very well be why Issei and Vali are so compatible with their respective Dragons.

By the way, I think that maybe even their prefences were opposites. Specifically, I think that Ddraig like boobs and Albion liked butts, which will furthermore explain Issei and Vali's compatibility with Ddraig and Albion. Though, then again, when Issei talked about sucking on Rias's Oppai, Ddraig seemed kinda down on that, so maybe Ddraig was actually the one liking butts, and Albion liking boobs, which will also make sense why Albion was down when he was called Ketsuryuukou.

I also heard about some theory that says that Ddraig and Albion started fighting over whose fetish was better, and God made it so they will have hosts with the oher fetish, lol. But then again, it kinda doesn't make sense when you think about the girl hosts. Unless, lol, they were lesbos, in which case it still would make sense, but I don't know if Ishibumi would go this far... lol.