Oheyama is a supporting character in the anime film Chinpui: Eri-sama Katsudō Daishashin. He is a sixth-grade student in the same school community as the main characters, and while the film credits identify him simply as Oheyama, his full name is given as Masao Oeyama. He is a strong-willed boy whose most notable trait is his athletic ability; he is good at sports and confident in his physical strength. In everyday school life he tends to use that strength to push others around, and his most consistent behavior is bullying Sho Uchiki, the studious classmate who is weak at sports.

Oheyama's motivations are not a focus of the story. He functions as a typical schoolyard antagonist within the ordinary settings of the film, and he does not play a role in the central events involving the alien Chimpui, the stolen photo album, or the film production that forms the core of the plot. His role in the story is therefore that of a secondary figure who belongs to the everyday world of Eri Kasuga and her classmates rather than a character who drives or changes the narrative.

His key relationship is with Uchiki, whom he bullies, while his connection to Eri is that of a classmate who makes up part of her school environment. He is a different boy from another student, Masao Koyama, whose name closely resembles his own. In terms of abilities, Oheyama possesses no special or supernatural powers; his strengths are entirely ordinary and physical, centered on athletics and raw strength. He remains a consistent presence throughout the film, with no significant personal development or change in his behavior.