you dupe katanas the same way you do any other sword, cept have a Samurai have two swords ability. Have a shield in the up hand and the katana in the lower hand.....go to a store and hit the best fit button....change whatever sword it replaces the shield with for the broad sword (to save money) and tah dah! you should have a duped katana. (then again its been a while since I have played FFT but I know it works)