Travelers who reach the required Adventure Rank and complete the prerequisite quests will be able to use a Story Key to unlock Hangout Events for Sayu and Thoma.
The Story Quest feature is unlocked at Adventure Rank 26. Story Keys are obtained by completing Daily Commissions (one Story Key is awarded for every eight commissions completed.)
 

〓Quest Start Time〓
Permanently available after the Version 2.2 update
 

〓Series III Unlock Criteria〓
Adventure Rank 30 or above
Complete the Archon Quest "Chapter II: Act III - Omnipresence Over Mortals"