Defeat Angry Draguana in the Celestine Caverns. Then, talk to Alchemist Lancaster in front of the Marauder. Use your quest tracker to see your progress.
Alchemist Lancaster: I'll make the medicine now. It'll take some time. Alchemist Lancaster: Could you do me another favor in the meantime? NakanoAzusa: Absolutely, I'll just get tired if I laze about doing NakanoAzusa: nothing. Go ahead. Alchemist Lancaster: Some of the Draguana in the area have been Alchemist Lancaster: disturbing me. I can't even walk around without Alchemist Lancaster: getting harassed. NakanoAzusa: Got it. I'll clear them out of here for you. Alchemist Lancaster: Thank you. I'll get started on your medicine.
Reminder Dialog
Alchemist Lancaster: I'm worried if I'm asking you for too much just for Alchemist Lancaster: making the medicine. NakanoAzusa: No problem. Please just focus on the medicine.