 In January 1869, Yoshihara was baptized as a Christian at the Owasco　Outlet　Dutch　Reformed　Church shortly before he was accepted into Yale University in New Haven, Connecticut in 1869, where he studied political science and law.Following the Meiji Restoration, he accompanied Ōyama Iwao, Shinagawa Yajirō and Nakahama Manjirō to Germany in 1871 during the Franco-Prussian War as official military observers, visiting Frankfurt, Berlin and calling on Paris during a ceasefire.Returning to Frankfurt, the delegation purchased modern currency printing machines, which were used by the Meiji government to print its first banknotes.