Krana

"Beware the Krana! When worn, they can steal the mind... and not even a Toa might be able to resist their power."

- Turaga Vakama, Comic 4: The Bohrok Awake

Each Bohrok contained a parasitic Krana which acted as its brain and gave it its power. The Krana, besides controlling the Bohrok, provided the intelligence to the swarms.

History
The Krana were telepathically guided by Cahdok and Gahdok, twin queens of the Bohrok swarms. Without them, the Krana would not be able to operate to their fullest performance.

The Krana, while the Bohrok's power, was also its weakness: even the strongest Bohrok, without its Krana, became little more than an empty shell, which could then be programmed or trained to repair the damage it inflicted. One of the main functions of the Bohrok Va scouts was to replace a Bohrok's missing Krana. If one felt threatened, it could eject from its Bohrok host; this left the host powerless, but if the Krana attached onto another being's face, it took control of that being's mind and assimilated it into the swarm.

The Toa Mata collected 48, and placed them into special slots in the middle of the Bohrok nest. This unlocked the hiding places of six sets of Exo-Toa armor and the lair of the two dreadful Bahrag twins. When the Bahrag were defeated, the Bohrok shut down and the Matoran collected, pitted and sealed all their Krana away.

Recently, the Toa Nuva were sent on a mission to free the Bahrag, so they could release the Bohrok to return the island of Mata Nui to what it was "in the Before-Time" as Lewa said.

Krana types
The eight types of Krana each had their own name and rank in the swarm:


 * Xa: Swarm Commander. They lead their Bohrok on their mission.
 * Za: Squad Leader. They have the ability to communicate telepathically with other Krana of the swarm and lead squads comprised of the remaining breeds below each. There are several Bohrok of this rank so that the swarm can be divided into smaller groups and thus provide the right Krana for any situation in all areas subjected to their search protocols. This Krana controlled Lewa and Turaga Matau for a period of time.
 * Vu: Surveyor. They can let a Bohrok fly short distances ahead of the swarm to confirm that the path is clear.
 * Ca: Clearance. They have strong defense shielding; these Krana spearhead the swarm's mission.
 * Yo: Mole. They use their Bohrok to tunnel through anything on the island.
 * Ja: Scout. They have radar-like senses that detect distant obstacles in the path of the swarm. When with a Vu, both Krana can work together to clear the way for the rest of their squad members. Vu can confirm if the path is clear, while Ja can detect in-path obstacles and therefore a squadron's early warning is doubled by this teamwork.
 * Su: Worker. They have colossal energy and inhabit the strongest of Bohrok. They are always around when brute force is needed.
 * Bo: Sentinel. They can see in the dark and serve as night-time lookouts and lead their Bohrok into the darkest places on Mata Nui.

Krana Colors
Each breed of Bohrok and Bohrok Va wore a different colored Krana. The Bohrok's Krana color corresponded with their colored eyes:


 * Blue: Tahnok
 * Orange: Gahlok
 * Red: Lehvak
 * Green: Pahrak
 * Yellow-Green: Nuhvok
 * Light Blue: Kohrak
 * Yellow: Tahnok Va
 * Purple: Gahlok Va
 * Dark Grey: Lehvak Va
 * Tan: Pahrak Va
 * Black: Nuhvok Va
 * White: Kohrak Va

Trivia

 * Coincidentally, the Ca breed of Krana was similar in appearance to the Kanohi Hau, which also had the power of shielding.
 * The Fohrok, unlike Bohrok, were not controlled by Krana.
 * The Krana would work just as well as a Kanohi on a Matoran's face to keep them awake and alive.
 * In the Metru Nui Archives, Toa Metru Whenua nearly knocked over an exhibit of Krana.
 * The krana each have a three letter code, written in Matoran, on the back. These codes have no story line importance and do not spell any real words.