Tataka said that your skills had improved so much that your weapon should be upgraded too. So you obtained Vorpal Essence, a Shulack Refiner and a Blessed Aurium Ingot, and went to the Jotun Studio. There, you made a crystal called Siel's Essence. You brought Siel's Essence to Tataka, who used it to upgrade Siel's Gleaming Sovereign Aether Key.