At the close of the Great War, Gilgamesh's father trapped a terrible spirit within a helm. That helm has been stolen, and it is your job to hunt down the thief and get it back.
You'll then need to do some traveling. Head to Port Jeuno and speak to Sanosuke at the Duty Free Shop. Then, go to Mhaura and talk to Phoochuchu at LFKDS. Next, go to Bastok Mines and open the door at J-6 for a cutscene. Last, go to Waughroon Shrine in Palborough Mines for another cutscene.
Go back to the Waughroon Shrine and trade the Banishing Charm to the burning circle. Inside the BCNM, you will have 30 minutes to kill three demon NMs: Gaki (blm); Onki (smn); and Rasetsu (drk). After killing the NMs, you get another cutscene involving a ninja named Ren. He gives you a key item called Charred Helm.
This quest is part of the samurai artifact gear quest series. The complete quest series includes: