Essay on the Penn Libraries' collection of juvenile pocket fiction (bunkobon) published in Japan in the Taishō period (1912-1926), centered around the most famous of these series, Tatsukawa Bunko (also known as Tachikawa Bunko). Explores the origins of this genre, the connection of Sarutobi Sasuke—this series's most famous protagonist,—to the birth of popular ninja culture, and the literary divides between Tokyo and Osaka as seen through the content of their respective juvenile series.