Onua

Around 100,000 years ago, Onua and the rest of his team were created on the island of Artakha. From there, they were transported to Daxia and awakened. The Toa were immediately told by Helryx of their destiny to be the guardians of the Great Spirit Mata Nui. The Toa were then trained by Hydraxon in combat. In one exercise, the Toa were made to escape Spinax, on another exercise, Hydraxon took the Toa's Kanohi and hid them across Daxia. The Toa spent all day attempting to retrieve their Kanohi, but were only able to do so when Lewa realized they were to work together, and thus did so.

Upon completing their training, the Toa Mata were sent to Karda Nui to protect its Av-Matoran residents from living lightning bolt Rahi, known as the Avohkah. Tahu and Kopaka then led the other Toa to the Codrex. After they entered it, the hatch sealed them inside, and the two Toa were forced to explain their situation to the others. They could not leave the Codrex, because the energy storm that now filled Karda Nui would kill them. They also told them that they had to enter Toa Canisters, since the Codrex could not support life. Pohatu was the first to enter them, where they remained for thousands of years. They were actually shot up into the sky and fell down into the ocean. They were originally intended to land on Mata Nui, then make their way to Metru Nui and reverse Mata Nui's sleep. However, something went wrong, and the canisters just floated in the ocean for a thousand years. It wasn't until Takua collected the Toa Stones of Mata Nui that the Toa were summoned to Mata Nui's shores.

The moment that Mata Nui fell asleep, the Toa Mata's canisters fell into the sea, supposed to head for the island that would later be named Mata Nui. From there they were intended to head down to Metru Nui, find a scroll in the Great Temple, and get started on awakening Mata Nui.

Onua on Mata Nui

Unfortunately, their canisters malfunctioned. They floated in the sea for the next 1000 years, until Mata Nui was near the point of death. Takua, on the island of Mata Nui, was the only reason the Toa Mata made it to the island at all: by collecting the six Toa Stones, made earlier by the Toa Metru, and using them to summon the canisters to the island. When they arrived, they had lost all of their memories.

Quest for the Masks

After Onua's canister landed on the shore of Mata Nui and opened, Onua rebuilt himself. He began digging a tunnel, and happened to dig straight into an Onu-Matoran tunnel. He met Onepu, who introduced him to Turaga Whenua. Whenua informed him of his mission: to collect several Great Kanohi Masks of Power and defeat Teridax and awaken the Great Spirit Mata Nui.

Onua met up with the other Toa Mata shortly: Tahu, Gali, Lewa, Pohatu, and Kopaka. They decided to split up to search for their Kanohi masks. During the course of the search, Onua saved Lewa from a Muaka and later from being infected.

Eventually the six all found all of their masks, and descended from Kini-Nuiinto Mangaia. They encountered the Manas, crab-like Rahi that they defeated by fusing into Toa Kaita. Onua became part of Akamai with Tahu and Pohatu; the other Toa became Wairuha.

The Toa then reverted back to their normal forms and encountered the Shadow Toa, dark versions of themselves. They eventually defeated them by absorbing their shadow counterparts into themselves. They then fought Makuta himself, disguising himself as a Matoran and then changing into a void of destruction. They defeated him by combining their powers.