Miyama Mizuha presides over the manga club at Kitanohashi High School. Her club shares contested territory with the neighboring magic club, fueling persistent boundary disputes. Mizuha actively campaigns to dissolve the magic club and reclaim their borrowed space, wielding bureaucratic leverage and intimidation tactics.

She commands fierce loyalty from her club members with her imposing and assertive personality. Her physical stature, particularly her bust size, frequently flusters Takeo Takakura, the magic club president, during their clashes, amplifying her intimidating effect on him.

Her history with Takeo stretches back to childhood, marked by her consistent teasing and bullying. This pattern continues into high school, often escalating their confrontations. Unknown to Takeo, Mizuha's enduring antagonism masks longstanding romantic feelings she struggles to express.

During the OVA storyline, her efforts to dismantle the magic club include reporting them to school authorities and direct confrontations with Takeo. She becomes an accidental casualty of magical mishaps when Akane Aikawa's spell causes flowers to bloom from her hair.

In the television series continuation, following the alien Bell's defeat and transformation into a massive cherry blossom tree blocking the city's sunlight, Mizuha pilots a blimp to launch negotiations with the tree, showcasing her proactive nature. Military forces ultimately thwart her attempt.

Her interactions remain dominated by conflict with Takeo and jealousy towards Sae Sawanoguchi due to Sae's closeness with him. Neither series offers significant character evolution or resolution for her romantic subplot.