A freshman and highly capable mad scientist. She was saved by Kodaka when she fell unconscious during a disastrous lab experiment, and begs to repay his kindness with sex; she joined the Neighbor's Club just to get closer to him. As a fujoshi, she is a passionate consumer of BL dōjinshi and magazines, is comically aroused by intercourse between mecha, and is delighted when Yukimura offers to have sex with Kodaka.

Although there are many adult themes in the series, she is the most sexually forward member. This was clearly highlighted in her first speaking appearance, when she described the attractions of rape to Kodaka in the middle of a stunned class. She has a habit of inserting any sexual innuendo possible in her sentences, to the point where she finds it normal to convert every innocent thought into something perverted. Rika is proud of her pervertedness, as she says that she would be a boring person if people only thought of her as a genius girl. To compound her eccentricity, she speaks in the third person.

In Volume 7, it was made clear that she's surprisingly the one who knows the most about Kodaka's feelings; seeing that he was just playing ignorant to their feelings despite fully well knowing them; as well as knowing his reasoning for doing so

In Volume 8, Rika agrees to be Kodaka's friend, making him the first friend she's ever got in her entire life.