Chizuru Sarashina, nicknamed Chi-chan, becomes classmates with Shuichi Nitori and Yoshino Takatsuki upon entering junior high. She possesses a notably tall stature, exceeding most girls and many boys, with a slender build, long legs, an oval face featuring a pointed chin, and dark brown oval-shaped eyes. Her dark gray hair typically flows in thin twin tails accented by medium gray highlights.

A free-spirit with an eccentric streak, Chizuru often acts impulsively without considering consequences, projecting a sometimes childish demeanor. She embraces unconventional behavior, like defiantly wearing the boys' school uniform or punk street clothes to school despite teacher objections, stating she does what she wants and disregards others' opinions. This impulsiveness sparks conflicts, particularly with Saori Chiba, who dislikes her unpredictable nature. Yet Chizuru feels genuine remorse when her actions cause trouble and actively attempts to make amends. She strives to befriend everyone and joins the girls' basketball team.

Her background includes a childhood friendship with Momoko Shirai, though Momoko often expresses frustration with Chizuru's behavior. Chizuru's family operates a soba restaurant. A defining moment occurs during a mixed-gender swimming class when she wears a revealing white string bikini, creating a startling contrast against the standard-issue tank swimsuits worn by peers. This act draws admiration from classmates but displeasure from teachers.

Chizuru provides steadfast support for Shuichi, especially after their absence following an incident where Shuichi wore a girls' uniform to school. Upon Shuichi's return, Chizuru walks hand-in-hand with them, deflects rumors, and confronts a mocking student. Later, when Shuichi seeks advice on presenting femininely, Chizuru avoids prescribing right or wrong, instead emphasizing that individuals should prioritize their own desires.

While not explicitly defined as transgender within the narrative, Chizuru displays significant gender non-conforming traits. She fluidly alternates between masculine and feminine presentations—such as school uniforms—and operates outside typical teenage gender boundaries. This fluidity contributes to her inclusion under the broader transgender umbrella in some analyses. Her Japanese name, "Chizuru," noted for its unisex nature and meaning "one thousand cranes," suits her character.