Aoi Shida, the third of the Four Shida Sisters and twin to Akane Shida, begins the series as a first-year middle school student. She possesses a delicate, slender frame standing at 4'9" tall, with less developed breasts compared to her eldest sister. Aoi wears her long black hair in twintails reaching her hips.

Her personality is shy, delicate, and highly feminine. Traditional hobbies like sewing occupy her time, alongside a strong passion for sweet foods, cute clothing, and dolls. Exceptionally virtuous, Aoi instinctively concludes she is at fault when things go wrong, blaming herself despite contrary evidence. This low self-esteem coexists with her consistently helpful nature, particularly toward those in trouble, reinforcing her supportive role.

Within her family, Aoi shares a close bond with twin sister Akane, often assisting her in school social situations due to Akane's difficulty befriending strangers. Aoi harbors feelings for Sueharu Maru, whom she affectionately calls "Haru Nii San," viewing him as a protective older brother. She experiences jealousy toward her eldest sister Kuroha over Kuroha's closer relationship with Sueharu.

Aoi plays a minor but observant role in key events. Following the Confession Festival incident, she and her sisters notice unusual behavior in Kuroha, specifically a sudden change in demeanor and habits. This observation leads them to suspect Kuroha suffers from amnesia, prompting Aoi and her siblings to inform Sueharu of their concerns, highlighting her attentiveness to family well-being.

Her name, meaning "blue" or "pale" (蒼) combined with "rely on" (依), follows the Shida family's color-themed naming convention. No significant character development or expanded background beyond these traits and events is documented in the available materials.