Kutsuki Masatsuna, also known as Kutsuki Oki-no kami Minamoto-no Masatsuna, was a hereditary Japanese daimyō of Oki and Ōmi with holdings in Tanba and Fukuchiyama. His warrior clan was amongst the hereditary vassals of the Tokugawa family in the Edo period. His childhood name was Tomojiro. Masatsuna was a polymath and a keen student of whatever information was available at that time concerning the West. Since most printed material was only available in the Dutch language, such studies were commonly called "Dutch learning". Dutch Japanologist Isaac Titsingh considered Masatsuna to have been his closest friend while he was in Japan, and their correspondence continued after Titsingh last left Dejima for the last time. The oldest surviving letter from Masatsuna to Titsingh dates from 1789; and this letter mentions mutual friends such as Shimazu Shigehide and Kuze Hirotami. Masatsuna and Titsingh shared an interest in numismatics. After Titsingh was reassigned from Japan in 1784, he sent packages of coins from India—Dutch coppers, as well as coins from India, Russia, Turkey, and Africa. Titsingh in turn received Japanese and Chinese coins as gifts. Masatsuna was an author of several treatises on numismatics. He was the first in Japan to circulate a book about non-Japanese coins with impressions taken from actual coins which had been obtained from Western traders. Masatsuna's collection of coins was brought to the UK in the 19th century, and is now in the British Museum and the Ashmolean Museum.
1781 : This numismatist scholar's book, Shinzen zenpu, was published.
1782 : This numismatist scholar's analysis of copper currency in China and Japan "Shinzen zenpu" was presented to the emperor.
1785 : This numismatist scholar's book, Kaisei kōhō zukan, was published.
1785 : Masatsuna inherited his father's position and titles.
1787 : This rangaku/numismatist scholar's book, Seiyō senpu, with plates showing European and colonial currency, was completed.
1789 : This rangaku/geographer scholar's book, Taisei yochi zusetsu, was published.
1800 : Masatsuna retires, handing over his position and titles to his son, Mototsuna.
1801 : Mototsuna predeceased his father, and Masatsuna's grandson, Tsunagata becomes daimyō.
1802 : Masatsuna dies.
1807 : Isaac Titsingh sends his last letter to Masatsuna from Europe, not knowing that his old friend had died some years earlier. Titsingh's decided to dedicate his translation of Nihon Ōdai Ichiran to Masatsuna.
