Gefeios said your skills have improved and you need a weapon to match. You obtained Vorpal Essence, a Special Shulack Refiner, and a Blessed Aurium Ingot. You then refined the materials at Jotun Studio and produced a crystal known as the Essence of Siel. When you brought the Essence of Siel to Gefeios, he turned your weapon into Siel's Dominant Greatsword.