Kenji Satō, a young boy with short brown hair often topped by a baseball hat, initially dismissed Muhyo and Roji's supernatural services as fraudulent—prompting him to vandalize their office sign. His skepticism toward ghosts shattered when he accidentally released a blood-drinking ghost that turned on him. Saved by Muhyo and Roji's intervention, his entire perspective on the supernatural transformed. Following his rescue, Kenji developed fervent admiration for the duo. He began frequenting their office, inventing excuses for visits despite Muhyo's rule against post-case client meetings without new business. He playfully nicknamed Roji "Sprout-Man" (or "Bean Sprout") and Muhyo "Onion-Boy" (or "Onion"). Mischief defines Kenji's personality: he delights in pranks and sports, showcasing natural athletic talent. He avoids studying, desk work, playing the recorder, carrots, and all onions. His skills include swift escapes and crafting practical jokes. In one instance, he reluctantly used his recorder-playing ability—a skill he normally shuns—to calm a ghost haunting his room. A pivotal moment reveals his growth: learning of a dangerous mission involving Muhyo and Roji, Kenji fears for their safety. He gives them his prized baseball cap as a talisman, extracting their promise to return it and ensure their survival. This act highlights his deep loyalty and emotional bond. As the series advances, Kenji's appearances become less frequent, particularly during story arcs unfolding beyond the city where the bureau operates. Nevertheless, his initial experiences and continued interactions solidify his role as a recurring figure connected to the duo's early cases and personal rapport.