Mari Ōaya is a supporting character in the anime film Magical Taruruuto-kun: Moero! Yūjō no Mahō Taisen. She serves as the homeroom teacher of the main cast, overseeing the fifth-grade class that includes Honmaru Edojo, Iyona Kawai, and their classmates. In terms of background, Mari is a young woman with a professional role at the school, and she is depicted with long blue hair that reaches her waist and blue-green eyes.

Her personality is defined by a strong-willed and strict demeanor during school hours. She holds her students to firm standards of behavior and is known for employing corporal punishment as a means of discipline whenever they break school rules, act out, or fail to follow policies. This authoritarian approach makes her a figure of both authority and intimidation in the classroom, yet it also underscores her commitment to maintaining order and teaching responsibility.

Mari's primary motivation is to uphold school discipline and guide her students toward proper conduct. She does not have personal ambitions or supernatural abilities; her authority comes from her position as a teacher. In the story, she functions as a conventional adult authority figure, often intervening when the children's mischief or magical escapades disrupt school life. Her role is largely episodic, as the film focuses on the friendship and magical conflicts of the younger characters.

Key relationships include her interactions with Honmaru and his friends, whom she frequently reprimands. She is not closely connected to the magical elements of the plot, but she represents the everyday school environment that contrasts with the fantasy adventures. Mari does not undergo significant character development; she remains a consistent, no-nonsense presence throughout the narrative. Her notable ability is her use of physical punishment to enforce rules, a characteristic that adds a comedic yet strict tone to her scenes. Overall, Mari Ōaya is a memorable supporting teacher who embodies discipline in the chaotic world of the film.