Ryōko Hanuki works as a dental hygienist, a profession contrasting her active presence within the social circle at Shimogamo Yusuisu. Slightly older than the main student group, she previously attended university alongside Seitarō Higuchi and Masaki Jōgasaki.

Hanuki possesses a heavy drinking habit; alcohol significantly impairs her judgment when intoxicated. Aware of this vulnerability, she carefully chooses her drinking companions. This caution manifests during group activities where her inebriation frequently influences her actions and decisions.

When the broken air conditioner remote triggers a time travel incident, Hanuki actively joins the mission to alter the past. Selected via rock-paper-scissors to travel back alongside Ozu and Higuchi, her involvement proves pivotal: she accidentally takes the functional remote to the present while wrapping it in cellophane, nearly creating a temporal paradox. This inadvertent action ultimately contributes to resolution by preventing universe collapse.

She interacts casually with the main group, often visiting the protagonist's apartment for its functional air conditioning. Her participation in Akashi's club film project demonstrates integration into their activities despite not being a current student. Shared university experiences establish her past connection to Higuchi and Jōgasaki, though specifics of her student years remain undisclosed.

Physically, Hanuki has an unspecified birthmark or mole. Her design reflects her adult status while maintaining visual cohesion with the university-aged cast.