The main character and narrator of the manga. Hideo has short black hair and a small build. He is the new Roman Club president, and is Kurumi's voluntary plaything. His physical strength and bravery are both lacking in the beginning. Kurumi uses her reward system to get Aiba to change his cowardly and lack-luster habits. As time progresses, his strength and endurance improve as Hideo jogs and works out to handle his frustration. Hideo maintains strong feelings for Kurumi, and does anything she tells him to do to get a "reward," going so far as to resist a judo arm-bar from the schools martial arts champ. His feelings lead to jealousy when other men grope Kurumi, or talk to her privately, or buy her things he cannot afford. This leads Hideo, along with his workouts, to strive for self-improvement.