Those are Reshiram and Zekrom, the legendary mascots of Pokemon Black and White. While I'm disappointed with you for not knowing that, the awesomeness of the image more then makes up for it.
They look pretty dang similar, for one, but that should be obvious just by looking at the picture. Zekrom is also an electric type with a few mechanical attributes, like Mechonis. Reshiram looks more organic, like Bionis.
Don't click on this if you haven't beaten Xenoblade, which means that only Assasin can click on it? How sad.
Zekrom and Reshiram are also similar in that they were being controlled (maybe "following" would be a better term for those two) by two people that believed in two different things. Zekrom sided with the Hero who fought for Ideals, while Reshiram fought for the Hero who fought for Truth.
The two dragons, and Kyurem, were apparently all one dragon at one point. This isn't really related to Xenoblade, but it felt important enough to be said.
Were you referring to the last sentence specifically, or the post as a whole?