Hm, I wonder, if referring to actual blades in the FF series..which one's would suit this end the best.

XI had the Lightbringer, its power is what caused Tavanazia's connection to the mainland to be destroyed, separating it from the rest of the continent. The sword, once unsheathed, released incredible power. I believe it was Ranperre who was the only one in XI history who could handle the sword unsheathed and control its power, thus how he took control over Vrtra.

The sword of darkness? I really dont know about that one.