Izumi Akazawa is a student in the third-year class of Yomiyama North Middle School, standing approximately 165 centimeters tall with reddish-brown hair typically styled into two ponytails. She becomes the head of the countermeasures committee for her class and later serves as the class representative. She is also a member of the drama club. Her personality is defined by a strong sense of responsibility and a straightforward, assertive nature, which naturally positions her as a leader among her peers. While she projects a tough exterior, this often masks a more fragile and tender side, and her impulsive temperament can lead to confrontational behavior. Her strong will is a prominent aspect of her character, though she is also capable of acknowledging her own mistakes. She harbors a hidden resentment toward Mei Misaki, partly due to a belief that Misaki failed in her duty as the class's non-existent person, which Izumi feels has endangered everyone. This resentment is also fueled by what she perceives as Misaki's effortless composure in the face of hardship, a stark contrast to her own struggles. A significant part of her background involves the loss of a cousin or older brother, who died as a result of the class's calamity. This traumatic event is a primary motivator for her to volunteer as the head of countermeasures, driven by a determination to prevent such a tragedy from happening again. She also has a prior, briefly forgotten connection to Koichi Sakakibara from a year and a half before the story begins, when the two met after the death of her relative and his aunt, leaving her with a lingering, positive impression of him. Over the course of events, she develops romantic feelings for Koichi.

In the story, Izumi is central to the class's efforts to combat the mysterious calamity. She is initially upset with Koichi for unknowingly breaking the class rules by befriending the non-existent Mei Misaki. As the leader of the countermeasures, she is responsible for enforcing the rules designed to appease the calamity, a role that becomes increasingly difficult and stressful as the death toll rises. She has a key relationship with her close friend Yukari Sakuragi in the manga, and with Takako Sugiura in the anime, and she deeply cares for her friends. Her friendship with Koichi evolves from initial irritation to a close bond as they work together to understand the curse. Her primary antagonistic relationship is with Mei Misaki, whom she blames for the deaths occurring in their class, insisting that Misaki is not doing enough as the non-existent person. Her development throughout the series is marked by a gradual descent into instability under the mounting pressure of the calamity and the loss of those close to her. She transitions from a composed and responsible leader to someone driven by fear, grief, and desperation. This is most evident in the anime, where, after the death of her friend Takako, she becomes convinced that killing Mei is the only way to end the curse and protect the remaining students. Ultimately, driven by this belief, she pursues Mei with lethal intent. Concerning abilities, no specific supernatural or physical abilities are noted. However, it is remarked that her hand is able to recall the impression of someone she once shook hands with. In the anime, her story concludes during a confrontation at a class retreat, where she is fatally impaled by shards of glass from a window shattered by lightning while attempting to save Koichi. Her last words, directed at him, express her wish that he remembered their earlier encounter, revealing her deep affection for him even in her final moments. In the manga, her fate is different, as she survives the series after being hospitalized. Following her recovery, she cuts her hair short and her personality appears to have softened, showing a regained sense of mental stability and even humor.