"Long ago, when the universe was still being born, the Great Beings realized that it required a core from which all energies would flow. In their great wisdom, they created a massive chamber that would provide power eternal for the Great Spirit Mata Nui and the universe he would rule. They named this chamber "Karda Nui," the Matoran phrase meaning "Great Heart.""
— Narrator, The Final Battle
|Position||Beneath the Southern Continent|
Karda Nui, also known as the Universe Core or the "World that Feeds the World", is the ultimate power source for the Matoran Universe, providing all light and energy used by Lightstones. The energy produced is sent to Metru Nui where it is redistributed to other areas of the universe. This energy is vital to the universe; if the flow stops, then health of the Great Spirit Robot begins to deteriorate. If all the light in Karda Nui is drained, the universe will be plunged into eternal darkness.
Before Mata Nui was created to watch over the Matoran Universe, Tren Krom maintained it from Karda Nui. When the Great Beings formed Mata Nui, Tren Krom was removed from Karda Nui and hidden elsewhere.
Karda Nui was once colonized by the Av-Matoran, and while they were there, the Toa Mata were assigned to guard the region. The Toa spent most of their time there defending the Matoran from sentient lightning bolts known as Avohkah. About 100,000 years ago, when their work there was done, the Av-Matoran left Karda Nui and inhabited the caves above it. It was around that time when the Avohkah were defeated as well.
Tahu and Kopaka tricked the rest of the Toa into going into the spherical structure known as the Codrex. At that same moment, the Great Spirit Mata Nui awoke for the first time. Tahu showed the others that Energy Storms were beginning in the giant cavern, and revealed that only the Toa Canisters would protect them. The Toa reluctantly locked themselves inside the canisters, and went into stasis.
During the Great Cataclysm, the Energy Storms came to a halt. Several of the stalactites on the roof broke off and fell to the floor, resulting in some of the the Av-Matoran villages in the caves above coming down with them so that the villages rested on the tops of the stalactites. The Matoran then rebuilt their villages and homes, and created jetpacks for themselves for travel between the locations. The stalactite housing the Codrex also fell, leaving the sphere resting in the swamp below the stalactites.
Vultraz eventually discovered the entrance to Karda Nui, but kept the location to himself. Vamprah, a member of the Brotherhood of Makuta, later found the entrance himself. Teridax, leader of the Brotherhood, ordered an invasion of the core. The strike force split into two groups, one which searched the swamps of the area, while another attacked the Matoran settlements by air.
Also during the Great Cataclysm, a hole in Karda Nui and the Southern Continent's roof was formed when Voya Nui rocketed from its position. As a result, sea water containing the Pit Mutagen entered through the continent's roof and dropped into the Karda Nui through the hole in the core's roof, forming a waterfall. The hole in the dome of the core was sealed when Voya Nui returned to its former position. Before the hole was sealed, however, Toa Mahri Matoro managed to slip into the core and use the Kanohi Ignika, reviving Mata Nui from death while sacrificing his life for the energy needed. Antroz, Vamprah, and Chirox, members of the aerial force, were blinded by the light released by the Ignika.
The Toa Nuva were teleported to the core by Artakha in order to fight off the attack. The Toa split into two teams, with one fighting alongside the remaining Av-Matoran while the other descended to the swamp below in an attempt to retrieve the Kanohi Ignika, which recently created a body for itself. The Order of Mata Nui stated that the organization relied on the Toa Nuva to prevent the invasion, and would provide them with any available help.
The Toa Nuva gathered the six Keystones scattered about Karda Nui, and used them to enter the Codrex. Completing their destiny, the Toa Nuva, with the help of Ignika, awoke Mata Nui. As a result, the Energy Storms began again, destroying everything and everyone inside.
Karda Nui is a massive dome, entirely enclosed, possessing no sunhole or stars. Fierce storms of energy are always raging within the chamber, a sign of the Great Spirit's vitality. The cave walls surrounding Karda Nui are virtually impervious, though one spot on the western wall that contains a portal to enter and exit from. Powerful shields protecting Karda Nui are meant to keep the Energy Storms from escaping Karda Nui and destroying anything outside of it. These shields can also block many incoming transmissions, such as the power of the Staff of Artakha, and Kanohi from a Suva. When the Energy Storms have dissipated due to the Great Spirit's weakening, the floor is covered in sand, and the environment is livable. The only structure present in the entire area is the Codrex.
After the Great Cataclysm, the severe structural damage to the Matoran Universe drastically altered the landscape of Karda Nui. Several massive stalactites fell from the ceiling of the core, and the Av-Matoran created villages on the tops of them. The dome filled with a thick mist, that was impervious to power of the Akaku Nuva. A hole in the ceiling, where Voya Nui used to be, created a Giant Waterfall, causing the floor to became a swamp with Pit Mutagen in it. This swamp section was known as the Swamp of Secrets.
All matter except the Codrex in Karda Nui was destroyed by the Energy Storms.
Most of the locations within Karda Nui were built in the absence of the Energy Storms, as the structures could not survive otherwise.
- Shadow Leech Hive (destroyed)
- Stalactite Villages (destroyed)
- Swamp of Secrets (destroyed)
- The Codrex
The Av-Matoran once colonized Karda Nui. Some Av-Matoran later returned to the core, after their homes were forced there by the Great Cataclysm. The Av-Matoran were formerly led by Kirop, although many of the Av-Matoran, including Kirop, were transformed into Shadow Matoran by the Shadow Leeches. All of them were later returned to being Av-Matoran by a Klakk. After doing so, they all evacuated Karda Nui and left to Metru Nui.
Below is a list of known Matoran which were residing in the core:
- Takua - Av-Matoran; later Takanuva, Toa of Light
- Tanma - Av-Matoran
- Solek - Av-Matoran
- Photok - Av-Matoran
- Radiak - Av-Matoran, former Shadow Matoran
- Gavla - Av-Matoran, former Shadow Matoran
- Kirop - Av-Matoran, former Shadow Matoran
The Rahi that originally inhabited the core, such as Air Serpents, were affected by energy spikes, but were defeated by the Toa Mata. The energy spikes were also contained by the Toa. There were some Rahi which inhabited Karda Nui after the Great Cataclysm, although they were not native to the core. Before the invasion, Av-Matoran made use of ScareRahi to keep Rahi away from the villages. All Rahi that remained in Karda Nui when the Energy Storms erupted were killed.
Some of the Rahi that inhabited the core are:
- Swamp Stalker
- Air Serpents
- A Klakk
- Various Rahi that were mutated by waters in Karda Nui's swamp.
- Tren Krom (formerly)
"In the world that feeds the world, of course. The wellspring of flame that blazes bright, yet burns none but its bearer. And he, oh, he it burns until there is nothing left, not even ashes."
— The Builder of the Toa Canisters, Dark Destiny
"The Toa's attention had been drawn to the powerful light coming through the gap in the continent. He had never seen such pure white light before, except when Toa Takanuva was in action."
— Toa Mahri Matoro's thoughts, Downfall
"Karda Nui – how to describe its glory, its wonder, its sheer beauty? How to capture the feeling one gets at the first sight of it? It isn't easy, but let me try.
It's a big cave. With a swamp in it."
— Makuta Mutran's thoughts, The Mutran Chronicles
"The place they created was more than just another cavern — it was so vast as to almost be a universe of it's own. Barren deserts stretched for hundreds of miles in every direction, and the roof of Karda Nui was so high above the ground it could barely be seen."
— Narrator, The Final Battle
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