For those who have not completed games in the Xenoblade Chronicles series, this page contains spoilers regarding the plot. Discretion is advised.
Erio is an NPC in Xenoblade Chronicles X. Erio is the Human appearance of HT665: Erio, and has a separate entry in the Affinity Chart. Erio's appearance and gender are determined when Definian Downfall is completed, being female if Cross is male, and male if Cross is female. They can be found by the round garden southeast of the Residential District's Cathedral, and later near the Barista Court in the Commercial District.
HT665: Erio will take the appearance of Erio after completing Definian Downfall. If Fortun was spared during this mission, they will inform the player that Fortun was stolen by another Definian named LV757: Lyvia and will ask the player to retrieve her, starting the mission Fortun and Glory. After completing the mission, they will spend their time on the Commercial District.