The daishō (大小 -"big-little") are a matched pair of swords worn by the Japanese Samurai.
The custom of wearing one long and one short sword is known as Nihonzashi , and began around the end of the Muromachi period (1333 - 1575) .
Before then, in the Kamakura period (1192 - 1332) Warriors would use the long bladed tachi that would be paired with a tanto, and later still the uchigatana would be paired with another shorter uchigatana.
With the advent of the katana, the wakizashi eventually was chosen by samurai as the short sword over the tanto.