Yoichi Nagumo is a prominent character in the manga series 'Sakamoto Days.' Known for his laid-back demeanor and exceptional skills, Yoichi is a former hitman who once worked alongside the protagonist, Taro Sakamoto. He possesses a sharp intellect and unparalleled combat ability, making him a formidable force despite his casual attitude. Yoichi's role in the series is pivotal as he provides insight into the world of assassins and often assists Sakamoto in navigating dangerous situations. His mysterious past and connections to other characters add depth to the storyline.