Julie, first encountered under the alias Chico, is a Native American woman of French descent met by the protagonist during his North American travels. She is the daughter of François Rochelle, a French diplomat and spy assassinated by Tenkai for his knowledge of Captain Kidd's treasure. After her father's death, Apache chief Geronimo adopted and raised her, integrating her into the tribe under her adopted identity.

The protagonist, Jiro, encounters her when she faces assault by outlaws; his intervention saves her and sparks their connection. She shelters Jiro with her tribe, aiding his recovery and quest. Julie guides him to Santa Catalina Island, the treasure's purported location, using her knowledge of the terrain and the geopolitical context linked to her heritage.

Following the climactic island confrontation where Tenkai appears defeated, Julie reappears under her true name, Julie Rochelle. She reveals her familial connection to the treasure hunt, confirming her father and Tenkai mutually killed each other years before—exposing Tenkai's use of body doubles to feign survival. She possesses a duplicate map matching Jiro's, confirming the treasure's location and emphasizing her inherited role in the conspiracy.

Julie provides crucial exposition, clarifying the international espionage conflict and the treasure's significance. Her mixed heritage and dual identity bridge cultural divides in the narrative, though her arc concludes after delivering these revelations.