Nuva Symbols

Created on Mata Nui when the Bahrag were sealed and the Toa Mata were transformed into the Toa Nuva, the Nuva Symbols were a set of unique stone carvings which the Toa Nuva used to temporarily house their core Elemental Powers for the continued stabilization of the seal they placed on the Bahrag after leaving the lair.

In the climax of their battle with the Bahrag, the Toa Mata combined their elemental powers to form a cage of Protodermis to immobilize the Bahrag. Since such a state of Protodermis is easily reversible by any input of external energy, the Toa Nuva devised a plan to house their elemental powers within a device to counteract any energy fluctuations bestowed on the Protodermis cage to break its state. Originally forming a sphere (the Nuva Lock), the Toa Nuva decided it would be the safest option to split this sphere apart into seven parts (the six Nuva Symbols and the central Nuva Cube), with the six Nuva Symbols being teleported to the Toa's respective Suva immediately and the central Nuva Cube remaining in the Bahrag's lair. This way, only the Toa Nuva could free the swarms (under unanimous decision, as a further failsafe in case one or more of them fall under the influence of Krana, Infected Kanohi, or other methods of mind control), and intruders to the Bahrag's lair would be unable to break the Protodermis cage without joining all pieces together first.

Since this system was a desperate solution to stop the swarms immediately, the ad-hoc design had an unforeseen critical flaw. Since the Toa Nuva invested their elemental energy into the Nuva Symbols to provide their function, and maintain control over them from the island's surface through the Suvas, removal of the symbols from the Suvas would cause the Toa Nuva to lose their elemental powers entirely by disrupting this system. This flaw was exploited by the Bohrok-Kal in their attempt to free the Bahrag queens.

In their final confrontation with the Bohrok-Kal in the Bahrag's lair, Tahu's use of the Kanohi Vahi mysteriously allowed the Toa Nuva to regain full mental control of the power they stored in the symbols, thus allowing them to unleash their power upon the Bohrok-Kal. The Bohrok-Kal were utterly destroyed in the process, and the Bahrag seal was preserved.

After the defeat of the Bohrok-Kal, the Turaga and Matoran hid the Nuva Symbols, so that future enemies (such as the Rahkshi) would not be able to find them. During the destruction of Ta-Koro, Tahu's Nuva Symbol was rescued and preserved, allowing him to maintain his Fire powers. The Matoran of Mata Nui took the symbols with them when they migrated back to Metru Nui, and later when they evacuated the Great Spirit's body onto Spherus Magna.

Trivia

 * While the Nuva Symbols were stated to be "likely" made by Artakha, this point was not necessarily worded as definitive canon as is therefore not convincing. As originally stated in the comics, each one was created on Mata Nui.
 * While the Nuva Symbols did not reappear in the 2015 BIONICLE reboot, their likenesses appeared on each Toa's armor.