Mio Nishizono originates from the visual novel *Little Busters!* and appears in the crossover anime series *Kaginado*, featuring chibi-style characters from various Key franchises. In *Kaginado*, her core characterization remains consistent with her original portrayal. She is calm, introverted, and diligent. Due to fragile health, she frequently carries a parasol during outdoor activities to protect herself from the elements. Her primary interest is literature, specifically boys' love narratives, and she often carries a book of poetry by Bokusui Wakayama. This literary preference informs her keen observation of interpersonal dynamics, particularly among male students, which she documents with notable enthusiasm.

Her background involves guilt over a forgotten imaginary friend. This friend manifests as Midori within *Little Busters!*'s artificial world. The parasol symbolically conceals her lack of a shadow, a physical trait resulting from Midori using Mio's shadow to materialize. In *Kaginado*, she interacts with characters from other Key works like *Clannad*, *Rewrite*, and *Angel Beats!*. Her role primarily aligns with her established persona: reserved yet observant, with her book and parasol serving as consistent visual traits. She appears only in *Little Busters!* and *Kaginado*.