Chika Aoki, the younger sister of Daisuke Aoki, lives in their hometown as a kindergarten teacher. She possesses violet hair and grey eyes. Outgoing, social, and lively, Chika contrasts sharply with her timid and quiet brother. She shows minimal reservations about physical contact and frequently teases Daisuke, though she generally treats others kindly—sometimes forcefully, like when assisting Mimi Usa with a tampon.

Chika exhibits strong protectiveness toward Daisuke, initially reacting with hostility to Kyōko Hōin over concerns about Kyōko’s suitability as a romantic partner for him in the city. This protectiveness arises from her deep affection and sense of responsibility for her brother. Her relationship with Kyōko shifts after a shared drinking incident where Kyōko, mistaking Chika for Daisuke, kisses her. This encounter also reveals Chika’s underlying desire for a male romantic partner, despite her popularity among women and lack of success with men.

During the summer OVA "Kodomo no Natsu Jikan," Chika eagerly anticipates Daisuke’s visit to their hometown with his students—Rin Kokonoe, Kuro Kagami, and Mimi Usa—and his colleague Kyōko Hōin. She observes the female companions closely, displaying delight toward the children but initial coldness toward Kyōko. The group spends several vacation days together by the sea.

Her name "Chika" combines the characters for "wisdom, intellect" (智) and "flower, blossom" (花), while "Aoki" signifies "blue, green" (青) and "tree, wood" (木).