The protagonist and central figure of the film, a seasoned taxi driver operating on the Tokyo to Hamamatsu route. He maintains a detailed diary documenting his daily encounters and passenger conversations. When two murders occur along his route, he realizes his passengers may hold crucial clues. His unique perspective and diary entries help uncover patterns and connections between the victims and suspects that the police missed. As he investigates, his own safety becomes a concern, driving him to assist in solving the case despite being an unofficial civilian observer.