Sakaashi (逆足) is a term used in the context of Japanese swords. It refers to a pattern where the ""Nie"" (沸) or the ""Nioi"" (匂) extends from the edge of the blade towards the tip, but in a direction that is inclined towards the tip. This pattern appears as a line connecting the temper line or scent from the edge to the tip of the blade.

The term ""Sakaashi"" translates to ""reverse foot"" in English, and it is named so because the pattern appears to be going in the opposite direction of the blade's tip. This feature is often seen in the works of the Rai school (来派) from the Kamakura period in the Yamashiro tradition.

In this tradition, there is a unique feature called ""Kyo Sakaashi"" (京逆足), where the ""Ashi"" is inclined towards the tang (Nakago) of the blade, which is the opposite direction of the tip. This feature is named so because it appears as if the ""Ashi"" is going in the opposite direction of the blade's tip, creating a unique visual effect.

Therefore, ""Sakaashi"" and ""Kyo Sakaashi"" add a unique and interesting visual effect to the blade, enhancing its overall aesthetics and value.