The yoroi dōshi (鎧通し), "fora armor" or "fora mesh", was a Japanese sword (nihontō) used by the samurai class as a weapon in feudal Japan.
The yoroi dōshi is a very thick tantō that appeared in the Sengoku ( late Muromachi ) period between the 14th and 15th centuries. The yoroi dōshi was designed to pierce armor and to stab while fighting in confined spaces.
The weapon ranged in size from 20 to 22 cm, but some examples may be less than 15 cm, with " tapered mihaba, iori mune, thick kasane at the bottom and thin at the top, and occasional moroha zukuri construction."
The motogasane (blade thickness) of the hamachi (the notch at the beginning of the cutting edge) may be as thick as 1.25 cm, which is characteristic of the yoroi dōshi.
The increased thickness on the back of the blade distinguishes the yoroi dōshi from an ordinary tantō blade.
Yoroi dōshi were worn inside the belt on the back or right side with the hilt facing the front and the edge upward.
Because it was worn on the right side, the blade would be unsheathed with the left hand, giving rise to the alternative name of (馬手差 metezashi) , or "horse-handed (i.e., left-handed) blade".