Ao Kajiwara is the younger brother of the main protagonist, Sora Kajiwara. At thirteen years old, he is a middle school student who stands in contrast to his older sister in several key ways. While Sora is known for her dreamy, quiet, and often unpredictable behavior, Ao is characterized by a much more grounded and pragmatic personality. He often serves as the voice of reason in his household, possessing a level of common sense and maturity that belies his age.

Despite being the younger sibling, Ao frequently takes on the role of caretaker, looking after Sora and managing many of the household chores. His relationship with his sister is defined by a deep-seated care and concern for her well-being, though he can also become visibly exasperated or bewildered by her singular and eccentric way of viewing the world. He makes a consistent effort to understand and sometimes regulate Sora's more unusual behavior, highlighting the quiet but strong bond of familial responsibility he feels.

Ao has a few specific personal attributes and preferences that round out his character. He was born on March 30th and has an A blood type. Standing at 152 centimeters tall, he has a fondness for Western-style sweets and enjoys playing video games. In contrast, he is noted to struggle with swimming and feels less comfortable with music, traits that help establish him as a relatable and ordinary young teenager. His role in the story is primarily to act as a foil to his sister's whimsical nature, grounding the narrative's more whimsical moments in the reality of everyday family life.