Katana

The Katana (sometimes also incorrectly called the Hayabusa sword) is a special armor permutation unlockable by earning every achievement (1000 gamerscore in Halo 3 out of 1000) and all skulls (including silver skulls). The sword closely resembles Ryu Hayabusa's Dragon Sword, and is not usable by the player.

Characteristics
The Katana consists of a normal Hayabusa body armor with a Katana sword affixed to the back with a silver attachment, possibly magnetized.

Trivia

 * There also seems to be some markings on the handle of the sword, some characters looking Japanese.
 * The Katana resembles the first Dragon Sword Ryu gets in Ninja Gaiden, not the True Dragon Sword. Truthfully said, almost every Katana looks similar to those of Halo version.
 * The Katana armor, like Hayabusa armor, is either scorned or praised by the Xbox LIVE community. The Katana armor is often stated to be just a showcase achievement, having absolutely nothing to do with Halo 3 or the universe itself whatsoever.
 * The Katana and the Security armor permutaions both come with getting all 1000G in Halo 3. Because of this, some fans thought that the Katana should've gone with the Security armor instead of the Hayabusa.
 * It is to some considered the hardest armor that you can unlock. It is the high of many a gamer.