Nuva Cube

The Nuva Cube was a lock, specifically to the Bahrag's Toa Seal which they were trapped in by the Toa Mata.

History
When the Toa unleashed an attack by firing all their elemental powers on the Bahrag, it created a seal around them, with the Nuva Cube beneath it. The six Nuva Symbols also appeared at the Toa Nuva's respective Suva.

After the Bohrok-Kal awakened, they managed to steal the Nuva Symbols, which caused the Toa Nuva to lose their elemental powers, and they went back to the Bahrag's chamber to unlock the seal. However, the Toa Nuva then arrived, and Tahu tried using the Kanohi Vahi to stop them, but failed. The Toa then channeled their elemental powers into the symbols, which increased the Bohrok-Kal's powers. The sudden overload destroyed them. The Toa Nuva later returned to Mata Nui, where they were to awaken the Bohrok as part of their tasks on the Scroll of Preparations. They went to the chamber, unlocked the cube, and freed the Bahrag.

The Cube can be unlocked when all six Nuva Symbol latch into their respective slots.