Aiko Tachibana is the strict yet deeply caring homeroom teacher for class 4-1 at Aozora Elementary School. Her personality blends kindness with an unshakeable belief that no one is inherently bad. She possesses significant judo skills, enabling her to defend herself and her students against threats, including supernatural Makai Beasts.

Aiko develops feelings for Kyouji Yamino, the human identity adopted by the amnesiac antagonist Yaminorius III. This relationship deepens before she discovers Kyouji's true identity as the sorcerer Yaminorius, a servant of the Demon World. Profoundly shocked, she refuses to abandon her belief in his potential for redemption. She actively pursues his reformation, even using a megaphone during battles to appeal directly to him, urging him toward goodness despite his continued allegiance to demonic forces.

Her character arc centers on this persistent effort to reform Yaminorius. Even after his memories return and he fully embraces his antagonistic role, she continues advocating for his change. Her unwavering actions highlight her commitment to compassion and redemption, embodying her core belief in the possibility of goodness within every individual.