It's really not that important. Look at dragoon's Longinus, it could have been Whale Whisker or Kain's Lance, etc. If I had to make a hope/guess of drk's relic I would say Chaos Blade. For that matter blm's relic could have been Mace of Zeus. When you have so much to choose from you tend to pick what seems to fit in the long run. If samurai ever gets implemented I would say relic would be Masamune or Chirijiraden. Who can say?