Katana

The Katana (sometimes also incorrectly called the Hayabusa sword) is a special Armor Permutation unlockable by earning achievements  (1000 gamerscore in Halo 3 out of 1750, or at least 49 out of 79 Achievements. The Katana closely resembles Ryu Hayabusa's Dragon Sword, and is not usable by the player.  It is possible to obtain the Katana by gaining 1000 gamerscore or a total of 49 achievements in Halo 3 by getting the new Halo 3 update achievements (i.e. 990 and then unlocking the new "Double Double" achievement for an end result of 1015 will unlock the Katana).

Characteristics
The Katana consists of a normal hayabusa body with a Katana sword affixed to the back with a white attachment, possibly magnetized. The sheath of the Katana is grey and the handle is a reddish brown color. It is not possible to use this item during gameplay unless bungie agrees that you have done something awsome enough to be rewarded with the usable katana.

Disadvantages
Users have reported that like the Security Shoulders, the Katana can re-lock and unlock again. For example, having 980 gamerscore and obtaining an achievement worth 25 gamerscore may unlock them, but they can later re-lock themselves, requiring the player to obtain more achievements in order to unlock it again.

The way the Katana sticks up can reveal you if you are sniping however if it is shot you do not take damage. It also cannot be stuck by a grenade.

Trivia

 * The Katana is a traditional Japanese sword.
 * There seem to be some markings on the hilt of the sword resembling Japanese characters.
 * The Katana resembles the first Dragon Sword Ryu gets in Ninja Gaiden.
 * The Katana and the Security armor permutations both come with getting 1000 GS/49 Achievements in Halo 3. Because of this, some fans thought that the Katana should have gone with the Security armor instead of the Hayabusa armor.
 * There is a myth that the katana can be stuck with a plasma or spike grenade, this theory has been tested and is not true
 * It is considered by some players to be the hardest armor to unlock, along with the Security helmet, because of the difficulty of some of the game's achievements.
 * There are rumors that a player can be damaged "through" the Katana because it extends out from the player's back (i.e using a plasma grenade or sniping). However, these rumors were proven to be incorrect.
 * The Sword's color cannot be changed, so it is always gray with a red hilt and a white armor attachment.
 * Since the Katana is already slung over the right shoulder, the player equipped with the sword can no longer use this shoulder for weapons. Instead they use the left shoulder. It has also been observed that by slinging a Sniper Rifle over one's shoulder with the Katana, an X is formed.
 * There was recently a glitch discovered by two Halo 3 players, wherein the one received the Katana with only 965 Gamerscore in Halo 3. It seemed to randomly spawn and disappear in the first player's armor selection.
 * Oddly enough, if a player is carrying a back mounted weapon, the gun is slung under the Katana, and where the Katana joins the body, instead of over it. It would seem that it would obstruct the drawing of a weapon, or cause the Katana to fall off, but apparently, it doesn't.
 * The Katana is most popularly viewed with the Hayabusa Helmet and the Rogue Helmet.