Prism Sword is the first unlockable sword, and can be unlocked by completing the "Prism Key" achievement. The Prism Sword is functionally identical to the starting katana, but enemies killed with the Prism Sword leave multicolored bloodstains (Enemies killed in other ways, such as throwable objects or explosions, will use the standard red blood color). The color appears to be determined by the time at which the enemy was killed, as two enemies killed with the same slice will use the same blood color.
Swords are the main weapons used by the player in Katana Zero. The player starts with a default Katana in the beginning of the game, but can unlock 5 others via achievements. The unlockable swords can be switched in and out in the Government Lab level, which is unlocked after beating the game.