This page explains how to complete the Endwalker Main Scenario Quest "A Capital Idea".
This quest is available if you have completed the quest Sound the Bell, School's In.
Starting the Quest
Talk to Krile in Old Sharlayan to begin the quest.
Speak with G'raha Tia
Go northeast until you are in the main hall, then go southeast to leave the building. Use the Aethernet Shard to go to the Baldesion Annex. Enter the building and check on the Main Hall Entrance. Say Yes to enter the Main Hall. Talk to G'raha Tia to proceed. There will be a cutscene.
Enter the Command Room in Limsa Lominsa
Teleport to Limsa Lominsa and go east to where the orange arrow is pointing in the minimap. Talk to Zanthael and say Yes to enter the Command Room. There will be a cutscene. Before you depart Limsa Lominsa, you may wish to get a Glamour Prism
Speak with Raubahn in the Ala Mhigan Quarter
Teleport to the Lochs (to the Ala Mhigan Quarter Aetheryte). Go northeast to where the orange arrow is pointing in the minimap. Talk to Raubahn to complete the quest. There will be a cutscene.
Next Main Scenario Quest
After you complete the quest, talk to Maxima to accept the next quest: Best of the Best.