This page explains how to complete the level 90 post-Endwalker quest "A Dragon's Resolve".
Requirements
This quest is available if you have completed the quest King of the Mountain.
Starting the Quest
Talk to Varshahn in Deepspine (accessible from Garlemald) to begin the quest.
Speak with Alphinaud
You can ride a mount here, so be sure to do so. Go south and make your way to the end of the path. At the end, check on the Passage to the Vicus Messorum and say Yes to proceed. Go to the quest icon and talk to Alphinaud. There will be a cutscene.
Search for a Leakproof Container
Go south, then east, and check on the Sturdy Barrel in the eastern part of the orange circle.
Fill the Leakproof Container
Go northwest, then north, and check on the Passage to Fons Manalis. Say Yes to proceed. Then get on a mount and go north, and follow the path to the quest icon. Check on the sparkling Destination to proceed.
Deliver the Ceruleum-filled Tank
Ride a mount and go southeast to the quest icon on the map. Check on the sparkling Destination to proceed.
Wait at the Designated Location
Ride a mount and go to the quest icon the map. Check on the sparkling Destination to proceed. There will be a cutscene.
Speak with Alphinaud Again
Talk to Alphinaud to complete the quest. There will be a cutscene.
Next Main Scenario Quest
After you complete the quest, talk to Zero to accept the next quest: Paths Barred.