Museum of Fine Arts, Boston: Japanese Sword Guards. E-book. Formato PDF Okabe   -  Forgotten Books, 2017  - 

With the introduction of Zen modes of thought during the Kamakura (1190-1337) and Ashikaga (1337-1582) periods, the samurai embodied in the sword their supreme conception of honor and man hood. In the icy steel, born of fire, they saw revealed the mystery of Life, indivisible from that of Death.