Hasumi Ōba belongs to the Ebisugawa Public High School Astronomical Club. She consistently exhibits a polite and kindhearted demeanor and is frequently observed conversing with fellow club member Yuka Iseda. While generally calm, she occasionally projects a distinctly scary aura. Her activities within the club involve participating in various investigations and events. Notably, she played a key role in proving Izumiko Todayama's innocence when the Astronomy Club faced accusations of causing students to faint, an action instrumental in preventing the club's abolition. Official media, including seasons, OVAs, and spin-offs, present her character without exploring a background story, family history, or significant character development.