Tataru has a small favor for you and asks you to join her at the Diamond Forge.
This quest is available if you have completed the quest An Ending to Mark a New Beginning.
Starting the Quest
Talk to Tataru in the Rising Stones in Revenant's Toll in Mor Dhona to begin the quest.
Wait for Tataru
Exit the Rising Stones and go outside, and go north to where the orange arrow is pointing in the minimap. Go into the hallway and enter the first door on the right, then check on the sparkling Destination. 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 Lucia
Go to Ishgard and use the main Aetheryte or an Aethernet Shard to go to the Forgotten Knight Aethernet Shard. Go east through the doors behind Firmalbert and talk to Lucia to complete the quest. There will be a cutscene.
Next Main Scenario Quest
After you complete the quest, talk to Lucia to accept the next quest: An Envoy for Ishgard.