The Katana is a weapon introduced in Eternal Damnation, and featured exclusively in the original A Week in Paradise mod. It was very likely made by M@DJ@cK@L. When swung, it has about the same power as the Machete. Secondary fire actually throws the katana straightforward and will usually kill a regular bystander in one hit. If the Postal Dude stands right in front of an enemy and holds secondary fire, they will continue to throw swords infinitely until the person dies and the sword can move forward. In enhanced mode, the katana can be thrown infinite times from the player's hand in any situation.
In Eternal Damnation it was exclusive to multiplayer, though enemies in singleplayer use it, albeit unobtainable by the player. This variant is very different. Primary fire does 2 quick swings, and makes the screen glitch a little. Secondary fire swings the sword 3 times, but a bit slower and with a different-feeling swing. It is undroppable from the player's inventory and has a lot of power in its swing.