Tokugawa Ienari
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 (the father-in-law of the eleventh shōgun, Tokugawa Ienari) and Kuze Hirotami ("Nagasaki bugyō" or governor of Nagasaki port).