The first book including the word 'Bushido' in Japan was 'Koyo Gunkan (record of the military exploits of the Takeda family)' which is considered to have been written by Masanobu KOSAKA.
「武士道」という言葉が日本で最初に記された書物は、高坂昌信著とされる「甲陽軍鑑」である。