Aya Hirooka is a supporting character in the agricultural university setting of Moyashimon. She works part-time as a bartender and is recognized as a friend of Aoi Mutou, another prominent character in the series. Aya is also described as a cheerleader, indicating an energetic and outgoing personality. Her primary role in the story is tied to her workplace, a bar where the main group of characters often gather. It is in this setting that she provides information about her friend Aoi, specifically revealing details about Aoi's past and her involvement with the university's UFO club, including the circumstances of a past relationship. Through these interactions, Aya serves as a confidante and a source of backstory for other characters, operating slightly outside the main circle of students directly involved with microbiology. Her key relationship is with Aoi Mutou, as she is one of the few people who knows personal details about Aoi's life. Beyond her occupation and her social connection to Aoi, there is no further detailed information available about her background, personal motivations, character development over the course of the series, or any notable abilities.