Kuro Chi ( " 黒血" Literally meaning "black blood" ) is a technique that combines the powers of Busoshoku Haki and Tekkai. The practitioners would use Busoshoku Haki to harden their veins and use Tekkai to harden their muscles at the same time, thanks to this, the practitioner would gain an exetremly powerful defence. Naturally this technique requires a great deal of concentration to perform. When this technique is used, the practitioner's veins become visible and dark, which earned it the name "Black Blood" .