Mihari Oyama is a central character in the anime series 'Oniichan wa Oshimai!' She is known for her intelligence and determination. As the younger sister of the protagonist, Mihari plays a pivotal role in the story. She is a talented scientist who develops a formula that accidentally transforms her older brother into a girl, setting off the main events of the series. Mihari is depicted as caring and supportive, often helping her brother navigate his new life while balancing her own academic pursuits. Her character adds depth and humor to the series.