Textbooks detailing covert techniques used by ninja and written pledges about their secret missions were passed down for generations at the home of a ninja descendant in western Japan, according to an analysis of ancient documents found there.

Experts in Japanese history say the documents discovered in 2000 in Koka, Shiga Prefecture, are valuable because they prove that ninjutsu techniques employed by feudal Japan’s mercenaries involved in such missions as espionage, sabotage and assassination were handed down to the next generations in the city.

Koka and Iga in Mie Prefecture are widely known as the home of the two most famous ninja clans. Ninja gradually diminished during the Edo Period (1603-1868).

Among around 150 items found in the house of 79-year-old Toshinobu Watanabe, 17 are textbooks on such subjects as how to make poison or conduct night attacks. Of the 17, four were written in the 1670s and 1680s, according to research conducted by the Koka Municipal Government since last year.

For example, one of the textbooks on poison instructs ninja to put into wells powder made by burning lizards or tiger beetles that were believed to be poisonous.

Another one on sleeping medicines says that enemies will fall asleep when smoke is emitted by burning powder made from insect shells or tobacco.

As for ambushes at night, ninja are recommended not to approach enemies immediately after attacking them with weapons involving fire since they might become engulfed by the smoke.

The documents kept at the Watanabe home also show that ninja acquired various other skills such as gunnery, horse riding and magic.

The 150 sets of documents include copies of 10 pledges written between 1700 and 1829 that were submitted to a local feudal domain.

The papers show that the Koka ninja vowed to join the fighting in the event of an emergency in the domain and not to reveal their status as ninja even to their family members and friends, as their contracts were classified. Ancestors of the Watanabes were farmers and they worked on a part-time basis as ninja under cover.

Masayuki Ito, a researcher at the Koka Board of Education, said a person hailing from Koka managed five ninja families, including the Watanabes, and secretly concluded contracts with the domain.

In peacetime, those “nonregular” ninja paid an annual visit to the Owari Domain in what is now Aichi Prefecture ostensibly for the purpose of gunnery instruction, he said.

Yuji Yamada, a Japanese history professor at Mie University, said the documents found at Watanabe’s home are “authentic historical materials” as many of them have been accurately dated and passed down in the family of ninja descendants.

KEYWORDS history, Ninja, documents