Miyashita is a supporting character in the anime and manga series Mitsudomoe. She is a student in Class 6-3, known for being noticeably tall among her peers and possessing a laid-back, sporty personality. She is described as the only well-adjusted student in the class, yet she has not fully grasped that good intentions can lead to unintended consequences. Despite her self-perception as the most normal student in the room, her persistent and somewhat desperate attempts to befriend the reserved and eccentric Hitoha Marui often come across as odd, leading other classmates to question her claim of normality.

Her primary motivation is to form a friendship with Hitoha, a goal she pursues repeatedly but usually fails to achieve. This effort highlights a caring and determined side to her character, even if her methods are not always effective. Outside of this pursuit, Miyashita is a loyal and close friend to Miku Sugisaki and Yuki Yoshioka, with the three forming a tight-knit group often seen together. She is generally helpful, friendly, and unassuming, though her height makes her stand out visually. Her appearance is noted to change when she lets her hair down, suggesting a different look that is rarely seen.

In the story, Miyashita functions as a member of the larger cast, providing a more balanced and grounded presence amid the chaotic antics of the Marui triplets and other classmates. She does not display any special abilities beyond being athletic, and her role remains consistent throughout the series without significant personal development arcs. Her relationships center on her close bonds with Miku and Yuki, and her ongoing, mostly unsuccessful campaign to connect with Hitoha forms a running subplot that reinforces her earnest but often misguided nature.