Etsuko apprentices under detective Hanpei Hattori. Mitsuko Kohmyoji hires Hanpei and Etsuko to track down Jiro following his departure, driven by concerns over his unstable behavior and potential threat to others. Etsuko actively joins Hanpei in pursuing Jiro across multiple locations, forming part of the investigative team dedicated to locating and returning him to the Kohmyoji family.

She is present during the climactic events at the DARK organization's headquarters, escaping the destruction alongside Hanpei and Mitsuko. Her role extends into the sequel OVAs, where she remains affiliated with Hanpei's detective work and appears in the background during the conclusion of the Kikaider 01 OVA. In the crossover special *The Boy with the Guitar: Kikaider vs. Inazuman*, Hanpei is depicted actively searching for Jiro, reinforcing Etsuko's established connection to his investigations, though her direct onscreen participation within that specific story is not detailed.

No further expansion of her background, personal history, or character development occurs beyond these investigative capacities and group affiliations across the series and its sequels.