Sadu has opened the southern passage to Yanxia, where you will go to the House of the Fierce.
This quest is available if you have completed the quest In Crimson They Walked.
Starting the Quest
Talk to Hien in the Azim Steppe to begin the quest.
Speak with Gosetsu
Go south from here to reach Yanxia, then speak with Gosetsu.
Speak with Hien
Go southwest to where the orange arrow is pointing in the minimap, and talk to Hien. There will be a cutscene.
Speak with Alphinaud
Talk to Alphinaud to complete the quest. You can now attune to the Aetheryte in the House of the Fierce.
Next Main Scenario Quest
After you complete the quest, you will need to be at least level 67 to proceed to the next quest. After you reach level 67, talk to Alphinaud to accept the next quest: The Room Where It Happened. There will be a cutscene.