In the mid Kamakura period, as a result of emphasizing utility, the width of the blade became wider, which makes a difference in the width of blade at the base and at the top less, and swords have a rounded surface.
鎌倉時代中期になると、実用性を重視した結果、身幅が広く元幅と先幅の差も少なくなり、平肉がよくついてくる。