After you defeat the Hitoderons, you find Will in the Great Lakes Cave. He needs you to talk to Lon in Yunkou.
Sail to Yunkou
Leave Will's house and leave the town of Nirlake. Go south and look for the port at Freedom. Go there and get on your ship. Sail around the world. There are many places to visit where you can get free items, so look for those if you feel like it.
When you're ready, go to Yunkou, which is in China. Go into the inn and go into the door on the right. You will find Fyda, who is sick in bed. Then go to the building in the northwest of Yunkou and go into the room. Talk to the man and he says that Fyda needs Ginseng, but Lon Trading went out of business so you can no longer get any.
Go between the fruit-seller stand and the unmarked building to find the door to Lon Trading. Go upstairs and talk to Lon. Ask for Ginseng, then agree to make a deal with him. He says that he thinks his brother Wong bought Dragoon Castle and is buying and hoarding things at the castle. Agree to help find Wong. Lon gives you the Ginseng.
Equip the Ginseng and go to the doctor in the northwest of Yunkou. Talk to him to find out how to use the Ginseng, then go back to Fyda's room in the hotel and give her the Ginseng. During the cut scene, say "That's not true!" After the cut scene, Fyda will say that you have to hurry to Dragoon Castle. go outside.
Perel is outside. Talk to him and say that you found out something. He'll say you need to get into Dragoon Castle. Leave Yunkou and go west to reach Dragoon Castle.