The longest and hardest element to upgrade in Ghost of Tsushima is your katana. You'll need astronomical quantities of materials, including gold, steel, iron, and other supplies.
Upgrading your katana will increase your damage.
Where to find iron and steel
Unfortunately, the options are limited to obtain large quantities of iron and steel. Most of the time, the best strategy will be to pick up everything on your path and hope for the best.
- Mongol occupied camps and territories are full of iron and steel. Search every yurt and browse the shelves and chests. This is by far the main source for these materials. You can find them in houses and villages to a much lesser extent.
- Carts of goods stopped by Mongols and bandits on the roads often contain large amounts of iron or steel. Remember to search the trunk in the back after killing the enemies.
Buy iron and steel
To our knowledge, there's only one NPC that sells these materials. All the trappers in the game sell components and tools, but Komatsu's is special. He appears only after you've liberated the town as part of the main quests with Yuna and Taka the blacksmith.
If you look at his merchandise, you can see that he sells a large amount of iron and steel, as well as some gold. You can sell other goods to get the supplies you need for your purchases.
Original content by Robin "Raiden" Bouquet.