Etsuko Sarutobi serves as apprentice to detective Hanpei Hattori. Recruited alongside Hanpei by Mitsuko Komyoji to locate the android Jiro after he departs to avoid endangering Mitsuko and her brother Masaru, Etsuko actively participates in the search and related investigations. She possesses brown hair cut short to ear length, black eyes, and typically wears glasses, a hat, a jacket, and sports spiky bangs.

During the climax at Professor Gill's headquarters, she stands alongside Hanpei and Mitsuko as Jiro confronts Hakaider. Escaping the facility's destruction with Hanpei and Mitsuko, she does not witness Jiro's fate. In the OVA special "The Boy with the Guitar: Kikaider vs. Inazuman," she continues assisting Hanpei in tracking Jiro. This results in Hanpei mistaking high school student Saburo Kazeda for Jiro. Etsuko witnesses the ensuing conflict involving Jiro, Saburo (who transforms into Inazuman), and a mysterious creature.

Her name honors Sarutobi Ecchan, protagonist of Shotaro Ishinomori's manga "Sarutobi Ecchan" and its anime adaptation. This intentional reference to Ishinomori's earlier work presents Etsuko as a normal human without the original Ecchan's supernatural abilities. Her role remains consistently supportive within investigative efforts surrounding Jiro's journey and conflicts.