Nodachi, Variant (3.5e Equipment)
From D&D Wiki
A Nodachi is a very sharp two-handed curved sword. Nodachi only have one edge, they are basically two-handed version of Katana. Nodachi are devastating against unarmored opponents but they lose potency against heavily armored opponents. Nodachi take a penalty to Attack and Damage against enemy with Medium or Heavy Armor (Mithral (or similar effect) armor count as they original category to determine if the Nodachi take a penalty or not.). Against Medium Armor Nodachi have -1 to Attack and Damages, against Heavy Armor the penalty rise to -2.