Chihiro Onizuka first appears as an elementary school classmate of Ōno Akira and Yaguchi Haruo, widely regarded as the least physically attractive girl in school. She remains part of Doi Genta's social circle throughout their school years. Her family name, Onizuka, meaning "demon mound," is textually noted as potentially relating to her appearance.

She attends the same middle school as the main characters. Later, during high school, she attends the same all-girls school as Koharu Hidaka, confirming their ongoing connection. Her physical characteristics consistently include pink hair, with one source specifying dark pink hair and black eyes. Her personality lacks self-awareness regarding her appearance and exhibits a crass demeanor.

Her story extends into the sequel series, *Hi Score Girl DASH*. At age 28, depicted as an adult and married, she deliberately throws her wedding bouquet to Koharu Hidaka. This action stems directly from her stated concern for Koharu's well-being and romantic future.