After saving Kuro, the Divine Heir, from captivity in Ashina Castle, Wolf faces off with a powerful warrior who severely injures Wolf and leaves him for dead. Wolf is then rescued by the Sculptor, who fashions Wolf with the Shinobi Prosthetic.
Aside from replacing Wolf's severed left arm, the Shinobi Prosthetic comes with a Grappling Hook, giving you access to higher ground and other spots that would be otherwise unreachable.
As you make your way through Ashina, you'll begin to see circular markers on grapple points. Once a grapple point becomes within reach, the symbol will turn green, indicating you can grapple to it.
While on your mission you will find Shinobi Tools, which can be given to the Sculptor to fit them to your Shinobi Prosthetic. A variety of Prosthetic Tools can be found in the world, and each has situations that make them very useful. For example, the Loaded Axe allows you to break enemy shields. Using Prosthetic Tools costs Spirit Emblems.
You can equip up to three Prosthetic Tools within the Equipment Menu.