Textbooks detailing covert techniques used by ninja – Japan’s feudal mercenaries – and written pledges on their secret missions were passed down for generations at the home of a ninja descendant in western Japan, according to 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 ninjutsu techniques employed by ninja involved in such missions as espionage, sabotage and assassination were handed down to the next generations in the western Japan city. Koka and Iga in Mie Prefecture, central Japan, are widely known as the home of the two most famous ninja clans. Ninja gradually diminished in Japan’s Edo period, from 1603 to 1868. Among around 150 items found in the house of 79-year-old Toshinobu Watanabe, 17 were 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 by the Koka city government since last year. For example, one of the textbooks on poison instructed ninja to put into wells powder made by burning lizards or tiger beetles that were believed to be poisonous. Another one on sleeping medicines said enemies would fall asleep when smoke is emitted by burning powder made from insect shells or tobacco. As for ambushes at night time, ninja were 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 home of the Watanabes also showed ninja acquired various other skills such as gunnery, horse riding and magic. The 150 sets of documents also included copies of 10 pledges written between 1700 and 1829 and submitted to a local feudal domain. The papers showed 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 city education board, said a person hailing from Koka managed five ninja families, including the Watanabes, and secretly concluded contracts with the domain. Forget Mario and sushi, Japan turns to ninjas to help woo more tourists In peacetime, those “nonregular” ninja paid an annual visit to the Owari Domain in what is now Aichi Prefecture, central Japan, 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.