Kozuka is the small knife stored in Kozuka Hitsu (groove of the sheath of the Japanese sword). Many Tsubas (handguard) have two holes to put Kozuka and Kougai (equipment for appearance) next to Nakagoana (a hole of the Tsuba to put sword),

so that Samurai didn’t need to draw his sword out of the scabbard when he wanted to use Kozuka or Kougai. Initially, Samurai used it for cutting wood or attacking enemies in an emergency. It is said that Kozuka was used as a craft knife rather than a weapon.