Chizuru Ōshima enters Syoyo High School as a timid first-year student with shoulder-length black hair, fringes obscuring her eyebrows, green eyes, and square-rimmed glasses. Academically diligent yet socially reserved, she battles low confidence and pessimism about her peer relationships. Hospitalization before enrollment delayed her integration, leaving her isolated as classmates formed early cliques. Elected class representative—a role she credits to her glasses—she struggles to assert herself, often yielding to avoid conflict. Her life shifts during Sports Day preparations when an upperclassman bullies her after an accidental volleyball pole collision. Haru Yoshida's intervention sparks her romantic interest, initiating emotional growth while she remains unaware of Haru's existing bond with Shizuku Mizutani. Shyness complicates her interactions, particularly with Haru; she copes by texting longtime friend Yū Miyama ("Yuu-chan") and using humor to manage anxiety. Despite her feelings, she encourages Haru's pursuit of Shizuku and advises him on understanding Shizuku's emotions, creating internal conflict as she secretly hopes for romance. This culminates in a school festival confession where Haru gently rejects her, affirming his love for Shizuku while unaware listeners watch. Chizuru distances herself but continues wrestling with unresolved feelings. Forced proximity to Haru's circle expands her social connections: Asako Natsume befriends her after noticing she eats lunch alone, and Sōhei Sasahara includes her in group activities like Christmas gatherings. She maintains a reserved dynamic with Shizuku, initially intimidated but gradually forming a tentative friendship after Haru temporarily leaves school. A subplot involves Shizuku's younger brother Takaya Mizutani, who develops intense infatuation, kisses her, and confesses. Chizuru sees him as a younger brother and initially rejects him, though the manga resolves their relationship with nuance. Her family runs a kimono store, and her name—meaning "thousand cranes"—references the Japanese legend of folding origami cranes for good fortune. Her blood type is A, a trait culturally associated with conscientiousness.