From Halopedia, the Halo wiki
The vertex was described as a pearly orb of Forerunner metal approximately the size of a Jiralhanae's fist that was embedded into a helmet-like device of similar material. The device is designed to be worn by Forerunners but can contort its shape to accommodate most users, including Jiralhanae and Humans. When the user puts on the vertex, it embeds itself into their skull and reconfigures itself to best function with the user's brain chemistry. This process is extremely painful and disorienting for the user, causing pain and sensory trauma such as flashes of light and a roaring within their mind. After fully accepting the vertex's integration, the user is able to control the Sharquoi's actions, as well as see, hear, and speak through individual Sharquoi. The process is not immediate, however, and the user is able to learn how to control the creatures more effectively. The process also washes away almost every facet of the user's prior personality and psyche, discarding it in order for the mind to be able to control a large number of Sharquoi. It is unclear exactly how much of the user is left after integration; it seems that their greatest desires and goals remain intact after the process. The vertex also stores a bit of every user's consciousness inside of it. As such, the current user can receive guidance and view memories from previous users. These essences can also act to incapacitate the current host if they feel that the vertex is in danger of being destroyed.
Beyond controlling the Sharquoi, the vertex has various other uses. Physical contact with it in the proximity of a Sharquoi hive will open the entrance, and after donning it the user is able to reveal the Sharquoi in storage and release them from their Stasis field. It can also repair neural tissue by burrowing deeper into the user's skull, allowing them to survive severe head injuries and even losing some brain matter. However, the vertex has some weaknesses; because it relays signals between the host and the Sharquoi via slipspace, a concentrated Electromagnetic pulse can disruptthat connection for a brief period of time. It can also be removed from the user's head relatively easily after being hit with that pulse, so much so that the feat is possible for a human civilian.
The vertex was built during the height of the Forerunner-Flood war by the Forerunners as a means to control the Sharquoi and use them to fight the Flood. Sometime prior to the Great Purification, the device was stored in the depths of Installation 00.
During the Battle of Installation 00 at the conclusion of the Human-Covenant War, the Jiralhanae Chieftain Hekabe led his war packs of the Voice of Maardoth into the underworld of the Ark in order to recover the vertex. Despite losing many warriors after the Flood's sudden appearance, they were able to recover the artifact and escape the Ark before the firing of Installation 08.
After agreeing to aid Thars 'Sarov in his attempt to oust his cousin Rojka 'Kasaan as the leader of the Sangheili on Carrow, the Voice of Maardoth arrived above Carrow and began to make their decent on the location of the Sharquoi hive. They invaded the human city of Suraka, which was situated above the buried hive, and began excavating the site until they found the entrance to the facility. Hekabe used the vertex to open the spire at the entrance and led his forces to the base of the structure. Upon reaching a citadel-like wall, Hekabe donned the vertex and allowed it to embed itself in him, which caused the wall to lower and reveal the Sharquoi being stored in statis fields. After fully accepting the vertex's embrace, Hekabe began releasing the Sharquoi who were now under his control and sending them to the surface to wreak havoc on the assembled Surakan forces. After emerging from the hive, he was able to commandeer several Surakan warships and killed his horde-captain Anexus for questioning his orders. Hekabe then spoke with Rojka through one of the Sharquoi before being struck in the head by a sniper round courtesy of Adriana-111 of Gray Team. Despite suffering severe injuries, the vertex was able to reconnect itself to Hekabe's mind and limit the damage. He was able to resume his attack on the Surakans in earnest, forcing Gray Team and Rojka to flee. He then fled back into the Sharquoi hive, taking a significant portion of his forces with him. He remained there and continued to direct the assault on Suraka via the vertex as well as using the captured Surakan ships to attack and gain control of Thars's fleet, giving him a ticket offworld. He continue to work unimpeeded until Gray Team, Rojka, envoy Melody Azikiwe, and Governor Ellis Gass attacked the hive and attempted to sever his connection with the Sharquoi. After a brief battle, this team reached Hekabe's position and used a M68 Gauss cannon with a HAVOK tactical nuclear weapon as a power source to fire an electromagnetic plus at the Jiralhanae. This severed Hekabe's connection with the Sharquoi and disoriented him, allowing Ellis to remove the vertex from his skull. She then put on the device, taking control of the Sharquoi. Ellis restrained Gray Team and Rojka before killing Hekabe before arming the Havok device in order to destroy the vertex and the remaining Sharquoi on Carrow. As the countdown on the nuke progressed, she began recalling the Sharquoi to her position, killing any Voice of Maardoth forces remaining in the city and in the captured Sangheili ships as well as hailing a Pelican for her team to evacuate from the facility. As the conciousnesses within the artifact tried to take control and prevent their destruction, Ellis manually detonated the Havok nuke, destroying herself, the vertex, the Sharquoi hive, and all of the Sharquoi remaining on Carrow.
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