Kō

Kō (硬 Temper) is the strong form of Gyō, where all of an individual's Nen-energy is concentrated into one particular body part. Zetsu is used to completely stop the flow of Nen in all other parts of the body. This makes that one body part exceptionally powerful, but leaves the rest of the body completely unprotected. This is used by some Nen-users as an offensive technique (a Kō-punch would carry all 100% of your Nen-power with it), but it is a risky move (leaving the rest of your body unprotected in a fight against another Nen-user is not generally a good idea).