Ōkubo Toshimichi
Nagai was born in Myōdō District, Awa Province in what is now Tokushima Prefecture, as the son of a doctor and started studying "rangaku" medicine at the Dutch Medical School of Nagasaki "(Igaku-Denshujo)" in 1864. While in Nagasaki, he made the acquaintance of Ōkubo Toshimichi, Itō Hirobumi, and other future leaders of the Meiji government.