Fuyumi Irisu is a second-year student at Kamiyama High School, where she is known among the student body by the striking nickname The Empress. Her family runs the city's hospital, a position that contributes to her notable reputation within the school. She is a tall young woman with a pale complexion, long, straight black hair, and indigo-blue eyes. Her appearance is marked by a white headband and a distinctive strand of hair that falls across her face to her right cheek.

Personality-wise, Fuyumi is portrayed as elegant, cold-hearted, and intensely pragmatic. Her primary focus is on achieving results, and she does not hesitate to manipulate others to get what she wants. This calculating nature is the source of her imperial nickname, reflecting her commanding and somewhat distant demeanor. Despite this formidable exterior, there are hints of a more awkward and pressured individual beneath the surface, a product of the high expectations that come from her successful family background.

Fuyumi's most significant role in the story is as the director of an independent film being produced by her class, Class 2-F, for the school's Kanya Festival. The film's original scriptwriter, Mayu Hongou, fell ill before completing the script, leaving the project's ending unresolved. The class wanted a murder mystery, but Hongou, who disliked death in stories, had written a script that did not align with this wish. Facing the potential failure of the film, Fuyumi took charge. She secretly sought outside help, eventually turning to Houtarou Oreki of the Classics Club under the pretense of asking him and his friends to simply watch the movie and give their thoughts.

She manipulates Houtarou's deductive abilities, guiding him to unknowingly create a new ending for the film, believing he is solving an existing mystery. Houtarou later confronts her, realizing that instead of solving a puzzle, he was writing one. Fuyumi does not deny the manipulation, revealing that she knew the original writer would not have included a death, but the class wanted one, so she needed a plausible mystery ending that didn't exist. This incident causes a significant rift, leaving Houtarou feeling used and angry. This arc highlights her core motivation: a relentless drive to ensure the success of her class's project, prioritizing the outcome over the methods used to achieve it.

Beyond this central conflict, Fuyumi has a key relationship with Eru Chitanda. Though their interactions are less intense, they appear to be on good terms, with Fuyumi even acting as a mentor of sorts. During the Kanya Festival, she gives Eru detailed advice on how to persuade people more effectively. She explains that one must encourage others to act of their own accord by making them feel mentally satisfied. For Eru, she suggests making people feel that she has high expectations of them. However, when she sees Eru awkwardly attempting to use this method, Fuyumi advises her to stop, stating that Eru's true strength lies in her straightforwardness, a quality she calls a peerless weapon. This interaction shows a more nuanced side of Fuyumi, one capable of genuine, if blunt, guidance.

Later, during the Doll Festival, Fuyumi participates in the procession, wearing the costume of the Emperor. She makes a point of speaking with Houtarou again, assuring him that this conversation is a simple, friendly one without any hidden motives, showing a possible desire for a fresh start or to make amends for her previous manipulation.

Fuyumi possesses notable abilities, primarily her sharp intelligence, strategic thinking, and a profound understanding of social dynamics. Her talent lies not in solving mysteries herself, but in identifying and utilizing the talents of others to achieve a desired goal. She is an excellent judge of character, able to recognize Houtarou's potential and orchestrate a situation that forces him to use his energy on her project. Her power is in her social engineering and her ability to remain composed and results-oriented, even when employing morally ambiguous tactics.