Tataka said it's possible to improve the Noble Siel's Supreme Spellbook. He said to gather Vorpal Essence, Special Shulack Refiner, and Blessed Aurium Ingot, then go to the Jotun Studio and fuse them together to create the Essence of Siel. You brought the Essence of Siel to Tataka, then he created the Siel's Dominant Spellbook.