The Real Ninja: Iga and Koga, the Ninja Manual Bansenshukai and the Shogun’s Secret Oniwaban
From Myth to Reality: Masters of Information and Survival, Not Assassins
Leaping across rooftops under cover of night, felling enemies with throwing stars and vanishing in a puff of smoke: through films, anime and games around the world, the ninja has become one of the most mysterious and fascinating icons of Japanese culture. Yet much of the familiar image, the black outfit, chain mail and straight sword on the back, is a product of fiction, dramatically exaggerated by Edo-period kabuki and storytelling and by twentieth-century manga.
Recent historical research and the study of old documents, especially work by the International Ninja Research Center at Mie University, have revealed a very different picture of the real ninja: experts in intelligence gathering and psychological warfare whose survival skills were built around one supreme goal, coming back alive.
In historical sources they were called shinobi, rappa, suppa or kusa. Their primary mission was not to assassinate enemies or attack important figures. It was to slip deep into enemy territory, gather secret information about supply lines, military roads, morale and alliances, and bring it safely back to their lord. They also carried out sabotage, setting fires inside enemy castles and spreading rumors to provoke internal division.
Above all, the most important rule was never to die. No matter how valuable the secret intelligence, it would never reach their lord if they were discovered and killed or forced to take their own lives. The martial skills and tools that ninja trained with were therefore designed not for killing but for avoiding combat, escaping and maximizing their chances of survival.
The origins of the ninja were closely tied to the yamabushi, the mountain ascetics of Shugendo. Training at the risk of their lives on rugged sacred peaks such as Yoshino, Kumano and Omine, the yamabushi mastered climbing techniques for scaling cliffs, a pharmacological knowledge of medicinal and poisonous plants, the ability to read sudden changes in weather, and breathing methods that allowed them to hide in the mountains for long periods with little food or water.
The local warriors of Iga and Koga applied these mountain survival skills to military and intelligence work, developing them into a practical system of ninjutsu.
What Made Iga and Koga Special: Self-Governing Communities That Defied the Warlords
Why did Iga, in northwestern Mie Prefecture, and Koga, in southern Shiga Prefecture, become synonymous with the ninja? The answer lies in their geographic isolation, as bowl-shaped basins surrounded by steep mountains, and in a social system that was highly unusual for the Sengoku period.
At the time, powerful warlords such as the Oda, Takeda and Uesugi were establishing absolute control over their domains. In Iga and Koga, however, there was no single dominant warlord. Instead, countless independent local landholders competed side by side. To resist invasion from outside, they formed sokoku ikki, egalitarian councils based on kinship and local ties.
Those who broke the rules were severely punished, and in an emergency, signals from bonfires and bells brought everyone together in an instant to form a line of defense. Their experience of guerrilla warfare in defense of self-rule, and harsh training in mountainous terrain, produced unmatched skills in infiltration, fortification and the mixing of gunpowder.
The unity and guerrilla strength of Iga's warriors were so formidable that in the Second Tensho Iga War of 1581, Oda Nobunaga had to send an army of more than 40,000 men in a campaign of total destruction.
Wisdom of the Bansenshukai: The Shoninki and the Art of Psychological Influence
In the peaceful Edo period, descendants of Iga and Koga ninja, fearing that their scattered techniques would be lost, compiled secret ninja manuals. The most important are the Bansenshukai, a comprehensive work written by Fujibayashi Yasutake in 1676, and the Shoninki, written by Natori Sanjuro Masazumi, a military strategist of the Kishu (Wakayama) domain.
These texts show that ninjutsu was not occult magic but a highly rational and practical form of psychology and behavioral science.
Ninjutsu was broadly divided into yonin, "open stealth," and innin, "hidden stealth." While innin meant sneaking in at night to eavesdrop, yonin meant disguising oneself in one of the "seven disguises," such as a traveling merchant, mountain ascetic, monk, wandering komuso priest or performer, then walking openly into enemy territory in broad daylight and drawing out information through conversation. It was, in effect, social engineering.
The manuals describe techniques of psychological influence based on classifying people as bold, timid, proud or lowly, humbling oneself before the proud and showing a threat to the timid to steer their minds. They also describe timing intrusions by an empirical understanding of human sleep cycles, entering at around 2 a.m., when people sleep most deeply. These insights into human nature still apply directly to modern intelligence work and negotiation.
The tools used by the ninja, called ningu, were also remarkably versatile and portable. The kunai was used less as a stabbing weapon than as an all-purpose tool, driven into gaps in stone walls as a foothold or used to dig through earthen walls to open a way in. Chains and folding grappling hooks were designed to fit inside the clothing, while bamboo devices were used for crossing water and breathing underwater.
Their tools were disguised as ordinary farming or carpentry equipment, so that even if a ninja was captured, he would not immediately be identified as a spy.
The Shogunate's Best-Kept Secret: The Oniwaban of Tokugawa Yoshimune
When large-scale warfare ended in the Edo period, many ninja served the Tokugawa shogunate as members of the Iga and Koga units, guarding Edo Castle and its gates. Separately, however, a new top-secret investigative body answering directly to the shogun was created: the Oniwaban, literally "garden keepers."
In 1716, Tokugawa Yoshimune, who came from the Kishu domain to become the eighth shogun, needed to push through the Kyoho Reforms against resistance from senior officials and hereditary lords. He brought seventeen families of foot soldiers from Kishu, including the Yakushiji and Kawamura, who were absolutely loyal to him, to Edo Castle. Officially, they were given the humble post of oniwaban, tending the plants and cleaning the Fukiage Gardens of the castle.
Their true mission, however, was to receive secret orders directly from the shogun, travel undercover to the domains of the daimyo, and secretly investigate the real state of local government, financial trouble, internal disputes and public discontent, then report directly to the shogun. The Oniwaban had the special privilege of meeting the shogun one-on-one and submitting their reports without going through senior councillors or inspectors. They never carried out dramatic assassinations.
They simply recorded accurate facts with cool detachment, serving as the shogun's eyes and ears and supporting the very backbone of shogunate rule.
Making the darkness of nature their ally, observing the subtleties of the human heart with a cool eye, and completing their mission alive: at the core of the ninja's skills was not violence but the ultimate intelligence of survival, avoiding ruin by controlling information.
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References
- Yamada Yuji, Ninja no Rekishi, Kadokawa Sensho, 2016
- Yamada Yuji, Ninjutsusho Bansenshukai o Yomitoku, Yoshikawa Kobunkan, 2020
- Natori Sanjuro Masazumi, Shoninki (annotated by Nakashima Atsumi, PHP Bunko)
- Fukai Masaumi, Tokugawa Shogun Seiji Kenryoku no Kenkyu, Yoshikawa Kobunkan, 1991
- Mie University Faculty of Humanities (ed.), Ninja no Shinjitsu, Kawade Shobo Shinsha, 2014
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