This page explains how to complete the level 86 Endwalker quest "Aether to Aether".
This quest is available if you have completed the quest Their Greatest Contribution.
Starting the Quest
Talk to Hermes in Elpis to begin the quest. There will be a cutscene.
Search for Hermes
Go southwest to where the orange arrow is pointing in the minimap. When you are close to the quest destination, use the Aether Compass (Main Menu > Duty > Collection) to find an Aether Current south of the quest destination. Then go north to the orange circle on the map. Go to the center of the orange circle and talk to Hermes to proceed.
Speak with Meteion and Have Her Accompany You
Go southwest to where the orange arrow is pointing in the minimap. There is an Aether Current east of the quest icon on the map, so be sure to attune to it before you proceed. Then go to the quest icon and talk to Meteion to proceed.
Search for Doros while Accompanied by Meteion
Go southwest to the orange circle on the map and attune to the Twelve Wonders Aetheryte. Then go northwest and talk to the Blond-haired Man. There will be a cutscene.
Speak with Meteion
Talk to Meteion to complete the quest.
Next Main Scenario Quest
After you complete the quest, talk to Hermes to accept the next quest: A Sentimental Gift.