I feel that Dragonbane and Goldbrand/Eltonbrand are somehow related but fail to explain their link.

Both are katanas whose fashion is reminiscent of the Akaviri crafting (actually, Dragonbane is likely to be of Akaviri fashion). But while Goldbrand was built to protect Dragons, Dragonbane was built to harm them. Are they ennemy blades, mirror sisters or something alike ? Is Dragonbane the "shadow" of Goldbrand, or the result of a trial to corrupt its power which would have led to the coming to existence of both a pure and an altered version of the blade (implying a minor Dragon break) ?

Does someone have any idea or clue to explain their strange similarity/antinomy ?