Entitled: "Suma". Print showing a musician playing the koto, while a warrior sneaks up behind the musician, drawing his sword from its scabbard. A ninja or shinobi was a covert agent or mercenary in feudal Japan. The functions of the ninja included: espionage, sabotage, infiltration, assassination and guerrilla warfare. Their covert methods of waging irregular warfare were deemed dishonorable and beneath the samurai-caste, who observed strict rules about honor and combat. Woodcut by Toyokuni Utagawa, 1853.