記憶術 Ninja Memory Techniques
From 武神館兜龍 Bujinkan Toryu by Toryu

Ninja Memory Techniques 記憶術 (Kioku-jutsu) by 山田雄司 Yamada Yuji for Hiden Magazine, September 2021 issue.
現代を生き抜く知恵を忍者の術と心に学ぶ!
Gendai o ikinuku chie o ninja no jutsu to kokoro ni manabu!
(Learn the Wisdom to Survive the Modern Era from Ninja Techniques and Spirit!)
Unlike the superhuman image shaped by manga and movies, real ninjas were highly practical masters of multiple skills. In this series, penned by Professor Yamada Yuji, a leading ninja researcher, we explore the latest research on the real techniques and spirit of ninjas to gain wisdom for navigating the present era!
Ninja Memory Techniques
記憶力は忍者の必須条件
Kioku-ryoku wa ninja no hitsū-jōken
(Memory is a Ninja’s Essential Requirement)

The 『軍法侍用集 Gunpō Samurai-yō-shū』 (Military Law Samurai Collection), compiled by Ogasawara Sakumo in the fourth year of Genna (1618), in the volume on theft, under “Third, Matters Concerning People to Be Sent as Ninjas,” states, “People to be sent as ninjas must be carefully selected,” listing, “First, an intelligent person. Second, a person with good memory. Third, a person with good speech.
Without talent and wit, one cannot become a ninja.” Thus, among the three essential qualities for someone sent as a ninja, memory is ranked second, and without that ability, succeeding as a ninja is deemed impossible.
Ninjas had to infiltrate enemy territories, accurately memorizing terrain, castle structures, weapon types and numbers, and the presence or absence of provisions. While it would be ideal to record what they saw or heard on paper at the time, there was often no opportunity, and being caught writing would be disastrous, so they relied on memory techniques to imprint information in their minds.
The 『当流奪口忍之巻註 Tōryū Dakuchi Shinobi no Kan-chū』 (Notes on the Current School’s Oral Ninja Volume), thought to have been established in the late seventeenth century, under “Matters of Mental Memory Catalog,” includes the following description:
“Whenever you wish to remember something, convert it into an object to memorize it well; there is a method to this conversion. If you always use common objects for conversion, you will forget them, so convert them into unusual objects instead. For example, if you want to remember ‘ink,’ imagine receiving a massive amount of ink on a specific day, month, and year from a certain place, exaggerating the conversion to memorize it. Why? Even in peaceful times, the Great Fire of Edo in Meireki 2 (1656) was such an extraordinary event that it’s unforgettable. Also, to memorize sequential items, associate them with the order of houses you know. If you don’t practice this diligently beforehand, it will be difficult to memorize in a hurry.”
Memorizing by exaggerating or associating with familiar objects is a method still used in modern memory techniques. Additionally, according to Kawakami Jinichi, the master of the Kōga Bantō lineage, there’s a technique called 「不忘の術 Fubō no Jutsu」 (Unforgettable Technique), where one strikes their fingers on a board to inflict pain or stimulation, and sometimes cuts their body with a blade to instill terror and memorize information, recalling it later by looking at the scar.
Even in daily life, seeing an old wound can trigger a cascade of memories, and modern neuroscience has proven that linking multiple pieces of information makes it easier to remember.
Memorizing by Associating with One’s Own Body

In the eighth year of Meiwa (1771), a book compiling memory techniques, 『物覚早伝授 Monozukuri Sōdenju』 (Quick Transmission of Memory), was published. It contains several memory techniques, and I’d like to introduce one.
Assign one to the crown, two to the forehead, three to the eyes, four to the nose, five to the mouth, six to the throat, seven to the breasts, eight to the chest, nine to the abdomen, and ten to the navel.
To memorize ten items—hand towel, brazier, hairbrush, inkstone box, koto, folding fan, writing box, mirror, pot, and teacup—imagine placing a hand towel on the first crown, associating the second forehead with the “hi” of brazier, linking the third eyes with the hairbrush for showing things, likening the fourth nose to a runny nose with an inkstone, comparing the fifth mouth to the koto of words, associating the sixth throat with a wide end if it passes through, remembering the seventh breasts with a writing box sealing the breasts, likening the eighth chest to a chest mirror, imagining the ninth abdomen swelling from eating a full pot, and picturing the tenth navel brewing tea.
In other words, it’s a method of memorizing by associating body parts with words or objects, but what to associate depends on one’s ingenuity. If there are twenty or thirty items to memorize, they suggest linking them to the left and right sides of the body, as well as the back or fingers.
Whether ninjas used this memory technique is uncertain, but it’s inferred they employed various memory methods to memorize enemy territory conditions. For ninjas, where a single numerical error could be fatal, accurately memorizing details was critically important.
Biography

山田雄司 Yamada Yuji. Born in 1967 in Numazu City, Shizuoka Prefecture. Professor at the Faculty of Humanities, Mie University. Graduated from Numazu Higashi High School, Shizuoka Prefecture, and the Faculty of Letters, Kyoto University. Worked at the Kameoka City History Compilation Office, completed the doctoral program in History and Anthropology (Interdisciplinary Japanese Culture Studies Curriculum) at the University of Tsukuba Graduate School. During his studies, he served as a lecturer for the Z-Kai Tokyo University Master Course and a Japan Society for the Promotion of Science Special Research Fellow. Holds a Ph.D. (Academic), served as a lecturer at Mie University Faculty of Humanities, and is currently a professor there. Research fields: Japanese medieval religious history, history of various beliefs. Formed a shooting club during university. Loves martial arts. Publications include 『跋扈する怨霊』 (Kikawahirobumkan, 2007), 『怨霊とは何か』 (Chūōkōronshinsha, 2014), 『忍者の歴史』 (KADOKAWA, 2016), 『忍者はすごかった』 (Gentōsha Shinsho, 2017), 『忍者の精神』 (KADOKAWA, 2019), and supervised 『そろそろ本当の忍者の話をしよう』 (Gambit, 2018), among others.
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Toda Gosuke is historically recorded as working in the Oniwaban intelligence agency as well as being a head falconer for the Shogun.




He was very excited about the finds and insisted that I get everything translated over into Japanese for him right away.