This page explains how to complete the level 80 post-Shadowbringers quest "Reflections in Crystal".
This quest is available if you have completed the quest Unto the Morrow.
Starting the Quest
Talk to Ryne in the Crystarium to begin the quest.
Speak with Beq Lugg
Go east up the stairs and talk to the Crystarium Gatekeep to enter the Ocular. Talk to Beq Lugg to proceed. There will be several cutscenes in sequence. If you are ready, say Yes.
Speak with G'raha Tia
Talk to G'raha Tia to complete the quest.
Next Main Scenario Quest
After you complete the quest, talk to Krile to accept the next quest: Alisaie's Quest. There will be a cutscene.