The term 'Assassin of Old Japan' refers to a NINJA, a type of covert agent or mercenary in feudal Japan. Ninjas were highly trained in the martial arts and specialized in espionage, sabotage, infiltration, and assassination. They were also known for their use of unorthodox weapons and tactics. Ninjas were often employed by samurai warlords and played a major role in the Sengoku period of Japanese history.