Naoko Mifune is a classmate of Tomo Aizawa and the best friend of Chiyomi Ogawa. She has dyed-red hair tied in a ponytail, with bangs that part in the center of her forehead, grey eyes, and freckles under each eye. Her initial encounter with Tomo is marked by jealousy and confrontation: she and Ogawa believe that Tomo is too close to Kousuke Misaki, an older student for whom both girls have a crush. This misunderstanding leads them to attempt to pick a fight with Tomo, but the situation is quickly resolved when Tomo clarifies that she has no romantic interest in Misaki and offers to support their feelings instead. From that point onward, Mifune becomes a friendly acquaintance rather than an antagonist.

Mifune’s personality is characterized by a quickness to jealousy, particularly regarding her crush on Misaki, but she is also able to change her attitude once the misunderstanding is cleared. She is not presented as having a particularly complex inner life or a strong individual motivation beyond her initial romantic interest and her loyalty to Ogawa. Her role in the story is that of a minor supporting character who helps to expand the social circle around the main trio, adding a brief moment of external conflict that is peacefully resolved. She has no notable physical or special abilities beyond being an ordinary high school student. Her development is limited: she goes from being a hostile rival to a neutral or friendly peer, but she does not undergo any significant personal growth or play a major part in the central narrative.