Tantō
Two tantō.
The tantō is a short-cut weapon similar to a one-blade or double-edged sword with a blade length between 15 and 30 cm (6-12 inches). At first glance it may be confused with a "little katana", but its design differs in such a way that we could never attribute such consideration. Although the aesthetics is identical, the design of the blade and the tsuka (mango) are substantially simpler.
Generally, for tag reasons, it bears on the obi (belt), although it could certainly be hidden with relative ease. Although the samurai's secondary weapon was the wakizashi (shorter version than the katana) or the kodachi (shorter version than the tachi), some samurai preferred tantō for the ease of their handling and as a complement to their melee martial arts . As a ceremonial object it extended during the new era, replacing the wakizashi or kodachi in the ritual of the seppuku or harakiri (a ceremony of suicide that the samurai realized with the objective to recover its honor after a dishonor). >
Depending on the model you can differentiate between tantō (with guard), hamidashi (with small guard) or aikuchi (without guard).
Wooden or plastic tantō also exist and are used for the practice of disarming techniques in traditional martial arts. Japanese-style styles that include the use of a tantō in their programs for the upper or lower grades are:
wiki