Sanpei Shirato (白土三平) was born Noboru Okamoto in 1932, a son of well-known leftist painter and activist, Tōki Okamoto, who was active in organizing a proletarian art movement during the 1920s and 1930s. In wartime Japan, to avoid persecution from the authorities, the Okamoto family frequently moved around the country to different places including Kobe, Osaka, and some rural areas where young Shirato experienced poverty and came in contact with ethnic minorities and other discriminated groups (i.e., burakumin) as a child.
Shirato debuted in 1957 with his manga, Kogarashi kenshi. Although his earlier manga were aimed at children, some of them already exhibited social concerns, including social marginalization of ethnic minorities, the struggles of people in the lower class, the socially oppressive power structure–all of which became prevalent motifs in his works. Stylistically, his earlier manga in the late 1950s inherited the postwar mainstream manga style—which consists of Tezuka-inspired, simplistic cartoony depiction of characters with large eyes. His style gradually changed throughout the 1960s, as observed in the shift of visual style in Kamui-den.