Yuudoku Ketsueki

Yuudoku ketsueki (ゆうどく'けつえき, lit. "toxic blood"), is a blood-borne hiden that all Ketsuekigasu clan members of blood type O possess. Each individual blood cell in the carrier's body contains a chakra coil, and and this enables his blood to channel chakra in the same manner as tenketsu. This ability was originally possessed as a kekkei genkai by the previous Ketsuikigasu clan, prior to the Bloody Mist years, but it seems that the founder of this new clan was able to grant it to his descendents in the form of a hiden. After losing this hiden, Kurenai later regained it as a Kekkei Genkai upon the isle of whirlpools after discovering a relic from her clan's ancient past.

Carriers of yuudoku ketsueki are able to transmit and release chakra through their blood and bloodstream, functionally granting them a secondary chakra network. This secondary network greatly increases their chakra control, and enables them to perform jutsu internally. By channeling yang chakra through their bodies, ketsuekigasu are able to heal their injuries and purify their bloodstreams of poisons and diseases. Doing so is a conscious activity, that requires a certain level of focus, but typically has better results than if the same healing techniques were being attempted on them by another shinobi.

A more powerful, albeit dangerous, benefit of this technique is that the secondary chakra network of a yuudoku ketsueki carrier provides them with an aptitude for opening the eight gates. As they grow and develop, yuudoku ketseuki carriers are trained to practice discipline and to keep their emotions in check. As part of this training, all ketsuekigasu are taught how to open the first two gates. Those that fail to reign in their emotions during this training invariably release the gates and perish as a consequence. More experienced ketsuekigasu ninja sometimes advance their gates training, learning to open additional gates for greater bursts of power.

If a carrier is in contact with any of their exposed blood, he can transmit chakra through it in the same manner as tenketsu. This allows carriers to expend greater quantities of chakra over a shorter span of time (if the need arises). This is typically used to create temporary bursts of speed and strength, but can also be used to rapidly create seals or traps using blood as a cataylist and reservoir for the necessary energies.

If the blood of a yuudoku ketsueki carrier covers the tenketsu of another person, that person's tenketsu become blocked until the blood is removed. This can impair or even disable the formation of jutsu by that opponent. If more powerful jutsu are attempted while so covered, the impairment imparted by the blood can cause serious injuries and permanent damage to the opponent's tenketsu, as the buildup of energies becomes uncontrollable and wreaks havoc on the body.

If the blood of a ninja or kekkei genkai user becomes polluted by the blood of a yuudoku ketsueki carrier, the foreign blood prevents them from controlling their chakra by creating large amounts of interference in their chakra network. This can impair, to outright prevent the use of jutsu or kekkei genkai depending on the concentration of the contaminant. Ketsuekigasu assassins typically target the main organs associated with the use of a particular kekkai genkai; they try to infect the eyes of their opponent if they are able to use dojutsu.