You can get the Uchigatana very early game without killing any boss. You have to get out of the first training area ruin of the game and make your way into Limgrave. You need to go to the Church of Elleh where you’ll find a location of grace. You need to go East from the church of Elleh. There is a castle there and a pilgrim from which you can pick up the item west Limgrave map fragment. Now, you can properly see the locations of Limgrave on your map.
Location of Uchigatana
To get the Uchigatana you need to go to Deathtouched Catacombs the location is shown on the map. You can go the east from where you picked up the Limgrave west map fragment. You’ll reach the Third church of Marika, right outside the Church of Marika you will see a mountain top and there is a Wind boost there that looks like the image shown below.
You need to use this Wind Boost and it will boost you up the mountain. There are 3 wind boosts that you’ll have to use one by one which will take you to the mountain top. Now, you just have to go west and follow the given location on the map and go to the Deathtouched Catacombs.
Once, you’ve reached the Deathtouced Catacombs, There is a door that will take you down to the catacombs first staircase will lead to a location of grace. You can choose to rest there and to use this location later for fast travel.
You need to make your way down to the catacombs, take a left and make your way to this location shown in the map. There are skeleton enemies in the catacombs you can choose to kill them or make your way straight to the location. While fighting the skeleton enemies remember once, you’ve downed they will regenerate so, you’ll have to hit them one more time to completely kill them. You’ll find a dead body there hanging by the ledge which is facing a tunnel. You need to pick up the item from the body. You’ll receive the Uchigatana from the dead body.