shuriken. The clay caltrops preceded makibishi caltrops. Archeologist Iwata Akihiro of Saitama Prefectural Museum of History and Folklore said the flat throwing stones "were used to stop the movement of the enemy who was going to attack [a soldier] at any moment, and while the enemy freezed the soldier escaped,". The clay caltrops could "stop the movement of the enemy who invaded the castle," These weapons were hastily constructed yet effective and used by a "battle group which can move into action as ninjas". Mie University founded the world's first research centre devoted to the ninja in 2017. A graduate master course opened in 2018. It is located in Iga (now Mie Prefecture). There are approximately 3 student enrollments per year. Students must pass an admission test about Japanese history and be able to read historical ninja documents. Scientific researchers and scholars of different disciplines study ancient documents and how it can be used in the modern world. In 2020, the 45-year-old Genichi Mitsuhashi was the first student to graduate from the master course of ninja studies at Mie University. For 2 years he studied historical records and the traditions of the martial art. Similar to the original ninja, by day he was a farmer and grew vegetables while he did ninja studies and trained martial arts in the afternoon. On June 19, 2022, Kōka city in Shiga Prefecture announced that a written copy of "Kanrinseiyo", which is the original source of a famous book on the art of ninja called "Bansenshukai" (1676) from the Edo period was discovered in a warehouse of Kazuraki Shrine. The handwritten reproduction was produced in 1748. The book describes 48 types of ninjutsu. It has information about specific methods such as attaching layers of cotton to the bottom of straw sandals to prevent noise when sneaking around, attacking to the right when surrounded by a large number of enemies, throwing charred owl and turtle powder when trying to hide, and casting spells. It also clarified methods and how to manufacture and use ninjutsu tools, such as cane swords and "makibishi" (Japanese caltrop). Oniwaban In the early 18th century, shogun Tokugawa Yoshimune founded the oniwaban ("garden keepers"), an intelligence agency and secret service. Members of the oniwaban were agents involved in collecting information on daimyō and government officials. The secretive nature of the oniwaban—along with the earlier tradition of using Iga and Kōga clan members