Yuzuru Nishimiya, the younger sister of Shoko Nishimiya and granddaughter of Ito Nishimiya, lives with her mother Yaeko Nishimiya in a single-parent household. A third-year junior high school student, she rarely attends classes, dedicating her time to photography. She developed this skill after receiving a camera from her grandmother Ito, teaching herself and winning first place in a local contest.

Her early photography focused on images of dead animals and insects, intended to demonstrate the gruesomeness of death and dissuade her sister Shoko from childhood suicidal thoughts. This protective role was ingrained by her mother Yaeko, who gave her a masculine name and fostered androgynous traits—including short black hair and typically male-coded clothing—to strengthen her perceived ability to defend Shoko. Her appearance often causes others to mistake her for a boy, a misconception she exploited by falsely presenting herself as Shoko's boyfriend to deter Shoya Ishida.

Yuzuru exhibits a brash, cold demeanor toward those she distrusts, initially directing this hostility at Shoya due to his past bullying of Shoko. She engineered his school suspension by photographing him retrieving Shoko's notebook from a river and sharing the image online. After Shoko confronted her over this incident, Yuzuru ran away from home; Shoya provided shelter, marking the start of their bond. Over time, she developed trust in him, eventually supporting his potential relationship with Shoko and confiding in him during her grief over Ito's death.

Her protective nature extends to monitoring threats, such as secretly recording Naoka Ueno's aggression toward Shoko with her camera. However, Yuzuru internalizes significant guilt, blaming herself for worsening Shoko's depression through her photography and for familial tensions. Her relationship with her mother Yaeko is distant and marked by resentment, partly due to Yaeko's emotional reserve. Yuzuru perceived her as uncaring until Ito's letter revealed their similar emotional coping mechanisms, prompting gradual reconciliation after Shoko's suicide attempt.

Following Shoya's recovery from a coma induced by saving Shoko, Yuzuru undergoes significant change: she abandons her focus on photographing death, returns to school to alleviate Shoko's worries, and seeks Shoya's academic guidance. This shift reflects her growing independence and self-discovery, influenced by Ito's final advice to prioritize understanding herself. She supports Shoko's decision to move to Tokyo for hairdressing studies, symbolizing her acceptance of their separate paths.