[Suggested] Complete [Essence of Tunta] Verti's Assistant

Mass of Pure Magic are used to enhance Blackstar gear. Upon completing the [Essence of Tunta] Verti's Assistant quest, you'll become appointed as an assistant of the Verti, the direct subordinate organization of Queen Viorencia Odore. You'll gain access to a special alchemy recipe to craft the Essence of Tunta, which you can exchange for Mass of Pure Magic.

You can find the questline by going to the window - Suggested tab - [Combat] [Lv. 60] Verti's Assistant Gets a Mass of Pure Magic?.