Yoroi-dōshi (鎧通し) is a Japanese single-edged knife, literally meaning "armor piercer."
The Yoroi-dōshi is a type of armor-piercing weapon designed for close combat. It is specifically intended to penetrate through armor. Yoroi-dōshi knives are not a separate category of weapons but rather exceptionally sturdy Tantō blades.
Some examples have a blade thickness of over 10 mm. The length typically ranges from about 22 cm to 29 cm. The Yoroi-dōshi was used, for instance, in duels or battles when a samurai had already brought down an opponent, allowing them to target the weak points in the armor by thrusting with this specialized weapon.