Hachū no Hataraki (刃中の働き) refers to the various patterns that appear within the blade of a Japanese sword as a result of the differential hardening process, known as ""Yaki-ire"". These patterns include ""Ashi"", ""Yō"", and ""Kinsuji"", among others.

""Ashi"" is a pattern that extends from the edge of the blade towards the tip, appearing as if it is pointing. ""Yō"" refers to an elliptical pattern that is scattered throughout the blade. ""Kinsuji"" is a thick, shining line that appears along the grain of the blade.

These patterns are created due to the differences in temperature and the amount of ""Yakiba-tsuchi"" (焼刃土) - a special clay mixture - applied to the blade during the hardening process. The temperature of the hardening process and the components contained in the blade also affect the formation of these patterns.

Therefore, ""Hachū no Hataraki"" adds a unique and beautiful visual effect to the blade, enhancing its overall aesthetics and value.