Miss Iijima is a female teacher who works at Tengen Academy, the school attended by the twin protagonists Ai and Mai Amatsu. In the novel adaptation her full name is given as Iijima Ryoko, while in the anime she is referred to simply as Miss Iijima. She possesses a youthful, doll-like face that contrasts with her tall, well-proportioned figure, and she wears a business suit that accentuates her model-like physique. She has long, straight brown hair that reaches her waist, with blunt bangs, brown eyes, and glasses, making her one of the few characters in the series to wear eyewear. Her appearance and composed demeanor earn her admiring and envious looks from the female students at the academy, who view her as an object of aspiration.

Her personality is described as earnest, modest, and gentle, with a faintly melancholic yet refined and pure atmosphere. She is a serious and responsible educator who cares deeply for her students. She had received some instruction regarding protective barriers from Genshu Amatsu, the grandmother of Ai and Mai. When the school's barrier is breached and chaos erupts on campus, she hurries to the twins and urges them to inform Genshu that the barrier was broken by an overwhelming spiritual force beyond her ability to counter. Later, she searches the burned ruins of the school and visits the storehouse to check on the safety of Ai and Mai, offering them kind words of encouragement when she finds them disheartened.

As the situation deteriorates, Miss Iijima is abducted along with a group of female students and shrine maiden trainees and taken to the demon realm. There she is made a sacrificial victim and subjected to relentless assault by Fujiwara no Tokihira. She is dragged before the Demon King by her hair, and when her white blouse is torn open, her exposed figure arouses the Demon King's lust. However, Tokihira intervenes, claiming that her matured body is unsuitable for the king and that she should serve as a vessel for instruction in depravity instead. She is then raped by Tokihira, an experience that inflicts upon her deep humiliation and lasting psychological trauma. The event in a carriage is particularly emphasized in the novel version as a source of profound shame and emotional injury for her.

Motivationally, Miss Iijima acts from a sense of duty as a teacher and a desire to protect her students, but her lack of combat ability leaves her powerless against the demonic forces. Her role in the story is that of a supporting character who represents the ordinary human victims caught in the supernatural conflict, and whose suffering underscores the threat posed by the antagonists. She does not develop supernatural abilities or undergo a transformation; her significance lies in her tragic fate and the way it affects the protagonists. Her key relationships are with her students, especially Ai and Mai, whom she tries to assist and comfort, and with the antagonist Tokihira, who becomes her tormentor.