Kongoutaika

It is the Kekkei Genkai of the Kengou clan from Konohagakure. It coats the user's body with a second “skin” that is virtually impenetrable—not even chakra can pass through—as long as it is unmarred skin. Using it on certain body parts is not very chakra-draining, but coating the whole body is. It also impacts the user’s stamina. Visually, the "adamantine" skin layer is dark grey, almost black. Full-body activation hides the user's hair, eyebrows, and transforms the eyes, which appear diamond-shaped. They can't speak when fully coated.