Weapons in Sekiro: Shadows Die Twice are limited to a set of Katanas that the protagonist wields in battle, and special tools for the Prosthethic Arm. In the screenshots of the box-art we also see the protagonist with a second katana on his back, but there is no dual-wielding.
Sekiro: Shadows Die Twice Weapons
The Wolf's Kusabimaru & Fushigiri
The katana is the only primary weapon, and the progression of gameplay is done by improving one's Skills rather than finding other or better weapons.
The secondary sword is called Fushigiri and has some relation to Kuro, the Divine Heir. This sword is used to deliver the final Deathblow to the undying-type enemies and Bosses encountered throughout the game. The final deathblow with Kusabimaru is called Shinobi Execution, if involving Fushigiri it would be called Immortality Severed, also in one particular situation it would be called Gracious Gift of Tears.