If you want the Uchigatana katana, you'll have to defeat the master swordsman who wields it. You'll find him near the top of Firelink Shrine. However, you don't have to fight him fairly. You can ascend carefully to the rooftops and then run along them. You should see the swordsman, running along the base of the wall, hoping to duel. From your vantage point, you can safely take him down with shots from the Soul Arrow spell. Just make sure you don't run out of magic in the process, or you'll have to drop down and finish the job the old-fashioned way.