Rikei Hiromatsu is a second-year student at Ebisugawa High School and a member of its basement-dwelling Astronomical Club. She has neck-length blonde hair and blue eyes, typically wearing her school uniform with stockings and occasionally a flower accessory. Rikei maintains a quiet, emotionless demeanor, passively following the club's activities and obeying orders—especially those from president Kyōko Todayama—without protest. Her defining trait is an intense cat fetish, demonstrated through interactions with the club's cat mascot Neko-sensei, whom she enjoys being rubbed against. This obsession escalates when she deploys an army of cats to confront student council president Yuka Iseda, who threatens the club's existence. During episodic events like investigating school-wide fainting incidents, Rikei participates consistently, adhering to her obedient nature and feline fixation.