Training

The skills required of the ninja has come to be known in modern times as ninjutsu, but it is unlikely they were previously named under a single discipline. Modern misconceptions have identified ninjutsu as a form of combat art, but historically, ninjutsu largely covered espionage and survival skills. Some lineage styles (ryūha) of ninjutsu such as Togakure-ryū are claimed to be descended from historical practices.

This diagram from the Bansenshukaiuses divination and esoteric cosmology(onmyōdō) to instruct on the ideal time for taking certain actions.

The first specialized training began in the mid-15th century, when certain samurai families started to focus on covert warfare, including espionage and assassination.^[60] Like the samurai, ninja were born into the profession, where traditions were kept in, and passed down through the family.^[23] According to Turnbull, the ninja was trained from childhood, as was also common in samurai families. Outside the expected martial art disciplines, a youth studied survival and scouting techniques, as well as information regarding poisons and explosives.^[61] Physical training was also important, which involved long distance runs, climbing, stealth methods of walking^[62] and swimming.^[63] A certain degree of knowledge regarding common professions was also required if one was expected to take their form in disguise.^[61] Some evidence of medical training can be derived from one account, where an Iga ninja provided first-aid to Ii Naomasa, who was injured by gunfire in the Battle of Sekigahara. Here the ninja reportedly gave Naomasa a "black medicine" meant to stop bleeding.^[64]

With the fall of the Iga and Kōga clans, daimyos could no longer recruit professional ninjas, and were forced to train their own shinobi. The shinobi was considered a real profession, as demonstrated in the bakufu's 1649 law on military service, which declared that only daimyos with an income of over 10,000 koku were allowed to retain shinobi.^[65] In the two centuries that followed, a number of ninjutsu manuals were written by descendants of Hattori Hanzō as well as members of the Fujibayashi clan, an offshoot of the Hattori. Major examples include the Ninpiden (1655), the Bansenshukai(1675), and the Shōninki (1681).^[8]

Some practitioners of modern ninjutsu include Stephen K. Hayes and Masaaki Hatsumi, who is the head (sōke) of Bujinkan, a martial arts organization based in Japan. However, the link between modern interpretations of ninjutsu and historical practices is a matter of debate.