Quon Kisaragi is a mysterious young girl who speaks the first words of the TV series and is shown meeting Ayato in episode 4. Her standard expression of surprise or agreement is "Ra-ra" (or "La-la") and most of her dialogue is cryptic and musically themed. She and Ayato do not connect romantically, but she displays a level of both physical and interpersonal comfort and intimacy with Ayato that is unmatched by any of the other characters, even Haruka. She is also one of the few people who never treats Ayato as a curiosity or an annoyance, and she seems to have an understanding of his situation and what his eventual role is, calling him Ollin ("motion" in Nahuatl).

Like Ayato, she has the marks of a potential instrumentalist. She and Ayato are both shown undergoing examinations, and while outside of her home she wears a vest-like device called a Life Module. Quon is skilled in playing both the violin and piano. She also is portrayed as curious about music that other people listen to on headphones, often taking them off to listen to the music.