The Tachi is a class 2 Sword in Salt and Sanctuary. It is an unusually light and graceful sword created using folded steel from Kar'hi, bearing a rippled pattern similar to that of ocean waves on the slightly-curved blade.
The Tachi can be found in a room with Split Swordsmen in the Red Hall of Cages; it can also be acquired by transmuting the Varangian Spatha with a Retchfeeder Maw, an Amber Idol and 3,500 salt. As implied by its description, it is a very fast-hitting weapon (nearly as fast as a Dagger), likely the reason why it is wielded by both Kesh Graydaughter and the Black Sands Sorcerer.
The Tachi is directly based on a real-world weapon of the same name.
Inventory description[]
"An unusually light and graceful sword crafted from folded Kar'hi'i steel. Its gently-curved blade bears an undulating, rippled pattern reminiscent of ocean waves."