Defeat Leeching vespers flying around in the Ashwood Trench to acquire 3 blood suckingvesper's hearts. Then, go to the Altar of Sahrar and talk to Juda Lucid.
Juda Lucid: Hm, earplugs, we don't need that. NakanoAzusa: We don't? What do you mean? Juda Lucid: You see Leeching Vespers in Ashwood Trench? NakanoAzusa: Yes, I do. Juda Lucid: Hunt them and take out their hearts. If we melt Juda Lucid: those with magic and turn them into liquid. All set. HiiragiKagami: That simple?!
Reminder Dialog
Juda Lucid: Why make things complicated? It's simple! NakanoAzusa: Oh, this isn't for me...