The Tachi was the customary single edged sword for the Japanese until the 10th century, when there was need for the Japanese horsemen to have a weapon for surprise attacks. During this time, the Tachi was shortened and called Katana to keep the distinction between the two. The Katana has always been known as the weapon of the Samurai, which were the guardians of Japan. Its thin blade and signature curved design distinguish it from other swords.
You may only use this Weapon of Choice if you are Duncan MacLeod. This weapon does not count against your Pre-Game limit. You may Attack to areas you just Blocked. Your Non-Special Attacks that cover only one grid do one less damage.