Akatsuki

The Akatsuki (暁, Dawn), supposedly an  grade sword, is a Chōkuto wielded by   Jim Hawkins. The sword, with its jet black sheath and guard-less hilt, is counted among one of the twenty-one finest katanas in the world and is known for its immense durability and unnatural sharpness. It is said Jim faced off against captain  in order to gain possession of the blade.

Abilities
The blade is said to tremendously augment its wielder's strength and the destructive powers of the user are greatly increased. Its durability is by far its greatest attribute and it was stated by Tashigi that its durability is easily in the league of the twelve Saijo O Wazamono. Another specialty of the blade is that due to the nature of the metal with which it was made it does not rust, neither does it ever loose its sharpness. Due to this same material's unique properties it is lighter, stronger, and sharper than most blades.

Trivia

 * While the article says that this sword is grade sword, this is just an assumption made by the wielder of the blade, in reality it is just on par with such swords and is only an exceptionally well made meito.