Kamakura period
Historically in Japan, the ideal blade of a Japanese sword has been considered to be the "kotō" in the Kamakura period, and the swordsmiths from the Edo period to the present day after the "Shinto" period focused on reproducing the blade of a Japanese sword in the Kamakura period. There are more than 100 Japanese swords designated as National Treasures in Japan, of which the "Kotō" of the Kamakura period account for 80% and the "tachi" account for 70%.