Defeat Deadly Diambi and Chaotic Diambi at Tagoul to obtain Hardening Oils. Give them to Merchant Taylor at Cirrugor. Use your quest tracker to see your progress.
Merchant Taylor: This leather is certainly of great quality, but too weak. NakanoAzusa: Weak? Merchant Taylor: Yes, it's too soft. The Marshal's suit must be highly Merchant Taylor: functional, meaning it must protect him well. This Merchant Taylor: leather cannot be used as it is. NakanoAzusa: But it wasn't easy for us to find this. Merchant Taylor: Oh! Leather hardener will do the job! Merchant Taylor: We need a hardener that will turn leather stronger. HiiragiKagami: Where do we find that? Merchant Taylor: This leather is very sensitive and the hardener I have Merchant Taylor: will ruin it. Have you seen those diambi floating about? NakanoAzusa: Yes, those dangerous monsters that float in the air! Merchant Taylor: When you defeat one, they leak a bit of sticky fluid. HiiragiKagami: Yes! That fluid ruined my blue dress! Merchant Taylor: That disgusting stuff is the best leather hardener around. Merchant Taylor: Could you get some of those for me?
Reminder Dialog
Merchant Taylor: It won't be much of a task for you, but will be tedious. Merchant Taylor: Please spare your time and effort for your Lord Marshal.