Nanako Saeki is a middle school student who serves as a central figure in the psychological drama of the narrative. She is widely regarded by her classmates as the ideal student: smart, popular, and physically attractive, with a composed and cheerful demeanor that makes her the object of admiration for many, especially the protagonist Takao Kasuga. Kasuga initially elevates her to the status of a pure muse and symbol of normalcy. Beneath this perfect exterior, however, Saeki carries a quiet sense of emptiness and a longing for something more substantial, which draws her to Kasuga’s apparent depth and mystery. After Kasuga defends her in front of the class, she agrees to date him, and a romantic relationship forms. This relationship becomes increasingly strained by Kasuga’s secret bond with the alienated classmate Sawa Nakamura, who holds a compromising secret over him. Saeki grows intensely jealous of the connection between Kasuga and Nakamura, and her feelings shift from gentle affection to a desperate, obsessive desire to reclaim his attention. She tries to compete with Nakamura’s influence through uncharacteristic, increasingly frantic actions, eventually reaching a point where she attempts to force Kasuga to choose her by seducing him and later destroying a hideout when she fails. Her role in the story represents the conventional world that Kasuga finds himself unable to return to, and she transitions from a passive object of admiration into a proactive, vengeful figure who is willing to compromise her own reputation in a futile attempt to hold onto him. Saeki’s development traces a path from innocent idol to traumatized young woman who must eventually reckon with the collapse of her idealized self-image. She is closely guarded by her best friend Ai Kinoshita, who becomes a fierce protector and later a bitter denouncer of Kasuga. In later years, Saeki moves on with her life, eventually starting her own family and reconnecting with Kinoshita, though the emotional scars of her middle school experiences remain. She has no supernatural abilities; her strengths lie in her social intelligence and academic competence, which initially make her the picture of success but prove insufficient to navigate the dark psychological terrain of her relationships.