The Tanto is the smallest of the Japanese Swords. Its blade measures about 12 inches and is very slightly curved compared to the Katana or the Wakizashi. This small sword was usually worn in the Obi belt of the Kimono and allowed an unmatched discretion and lightness.
Some samurai could wear it inside their Kimono to make it totally invisible to the enemy, it could then be used as a defense in an urgent situation or to stab an enemy discreetly.
Tanto is also known for the practice of Seppuku which is the samurai suicide ritual where the samurai would make a horizontal cut above his navel to forgive a non-honorable act or not to follow his master's order which he demanded immoral.