Tetsutoge (3.5e Equipment)
From D&D Wiki
The Tetsutoge is a mystical wakazashi used for trainging purposes. Though it looks like any other wakazashi, the grip of hit's hilt hides small, iron thorns that will cut into the hands of anybody who tries to wield incorrectly, such as by gripping the sword to hard or using brute force inplace of skillful strikes, dealing 1 damage forcing the user to make a Fortitude Save of 15 or else drop it from shock.
As a masterwork weapon, it grants it's wield +1 to all attack rolls made using it.