Katana

The Katana (sometimes also incorrectly called the Hayabusa) 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 attactchment, possible magnetised.

Trivia

 * There also seems to be some markings on the handle of the sword.