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.
 * It is to some considered the hardest armor that you can unlock. It is the high of many a gamer.