Now that you have settled matters in the Ruby Sea, you can now venture into Yanxia.
This quest is available if you have completed the quest Tide Goes in, Imperials Go Out.
Starting the Quest
Talk to Gosetsu in the Ruby Sea to begin the quest.
Journey to Yanxia
Go south until you can go southwest through the cave entrance (marked on the map with a green arrow). There will be a cutscene. This one is important, so it is recommended to watch it either now or via the Unending Journey in an inn room.
Speak with Gosetsu
Talk to Gosetsu to proceed.
Go southwest to where the orange arrow is pointing in the minimap. Talk to Gosetsu to complete the quest.
Next Main Scenario Quest
After you complete the quest, you will need to be at least level 64 to proceed to the next quest. After you reach level 64, talk to Gosetsu to accept the next quest: Life after Doma.