Akiko Yoshii begins her third year of middle school as the homeroom representative in Juri Kibayashi's class. She has brown hair and brown eyes. Akiko maintains a friendly, open-minded disposition and serves as the voice of reason, though her sensible advice is often ignored amid supernatural occurrences and her teacher's eccentric behavior. Her priority remains maintaining harmony among classmates and teachers, leading her to persistently mediate conflicts involving Kibayashi-sensei despite the teacher's unconventional methods and unfamiliarity with the living world.

Demonstrating responsibility and cooperation, Akiko helps coordinate class activities during chaotic situations caused by Kibayashi-sensei's supernatural experiments. She volunteers to assist classmates facing issues, including supporting Emma during sleep paralysis incidents. Akiko approaches each new school term with enthusiasm for potential experiences, reflecting her optimistic outlook. Her interactions reveal a preference for academic normalcy and stability, evident in attempts to prevent conflicts between Kibayashi-sensei and science teacher Nagara.

Akiko participates in standard school activities like physical examinations and classroom events, frequently navigating disruptions caused by Kibayashi-sensei's occult practices. She witnesses various supernatural events firsthand, including spirit possessions and the arrival of non-human transfer students. Her role consistently positions her as an audience anchor point, representing a relatively ordinary perspective within the narrative's extraordinary circumstances.