Merlwyb asks you to return to the command room in Limsa Lominsa to plan your attack on Leviathan.
This quest is available if you have completed the quest The Gift of Eternity.
Starting the Quest
Talk to Merlwyb in Western La Noscea to begin the quest.
Speak with Merlwyb
Go back to Limsa Lominsa and go east from the Aetheryte Plaza. Talk to Zanthael and say Yes to proceed to the command room. Talk to Merlwyb and there will be a cutscene.
Speak with Yugiri
Talk to Yugiri and there will be a cutscene.
Speak with the Storm Private
Use the exit, then go east to exit Limsa Lominsa via the Zephyr Gate. Go southeast and go through the gate to reach Lower La Noscea. Go east to where the orange arrow is pointing in the minimap, enter the building, and talk to the Storm Private. There will be a cutscene.
Report to Eynzahr
Exit the building and go southwest to where the orange arrow is pointing in the minimap. Talk to Eynzahr to complete the quest.
Next Main Scenario Quest
After you complete the quest, talk to Eynzahr to accept the next quest: Lord of the Whorl. There will be a cutscene.