Aoi is a minor but symbolically important character in the series, appearing as a cheerful and energetic young girl approximately six to seven years old. She has long dark brown hair tied into two ponytails, often adorned with a flower, and light brown eyes. Her typical outfit consists of a pink long-sleeved shirt, an orange dress with a white collar, a brown front knot, and pink sandals.

Aoi is the daughter of an unnamed woman and becomes the stepdaughter of Satoshi Oginome following his second marriage. This makes her the half-sister of Ringo Oginome and the late Momoka Oginome. She is first introduced in the eighth episode of the series during a family outing to an aquarium with her mother and Satoshi.

In terms of personality, Aoi is depicted as a lively and outspoken child who seeks attention from the adults around her. She runs around excitedly, speaks loudly, and eagerly shares facts she knows, such as pointing out a moray eel to her stepfather. Her behavior is spontaneous and unfiltered, as seen when she directly asks Satoshi if he would be willing to come to her school and pretend to be her biological father.

Aoi's primary role in the story is tied to her relationship with Satoshi Oginome and her symbolic significance to Ringo. She appears to be very fond of her stepfather, whom she addresses as Mister rather than dad, and is overjoyed when he proposes to her mother, jumping into the air with excitement. For Ringo, Aoi represents the new family that her father has built after the death of Momoka and the dissolution of the original Oginome family unit. In one of Ringo's hallucinatory episodes, Aoi is transformed into a seductive sea serpent coiled around their father, illustrating Ringo's distorted perception of her as a rival who has stolen the familial love she feels entitled to. This moment highlights how Aoi, while innocent in her actions, becomes a focal point for Ringo's feelings of abandonment and jealousy. No notable abilities are associated with this character.