Onua fell from the sky into the sea in one of six capsules with five others known as the toa. It would become their mission to free the island Mata Nui, where they washed up, from the grasp of the evil Makuta and save Mata Nui, the being for which the island is named.
Onua can control and produce earth with almost no limit. Extensive use of his earth powers in a short amount of time can drain him but he can absorb energy from the earth to regain his strength. He carries two giant claws for digging and to use as weapons. He posses the Great Kanohi mask Pakari that makes him extremely strong. He is very good at digging and spends most of his time underground. He can also see in the dark. His being is comprised of bio mechanical metal called protodermis, making him very durable. Because his earth abilities he was very attune to the ground and could feel vibrations in it, sensing the approach of others. It was sensitive enough for him to tell apart various animals and other toa.
Onua was a member of the toa team including Gali, Pohatu, Tahu, Kopaka, and Lewa. They arrived on Mata Nui unaware of who they were. They found villages of beings called Matoran who had awaited their arrival to free them from the tyranny of the Makuta. The Matoran were led by wise beings called the Turaga who knew the toas' names and purpose. It was their destiny to find all of the great Kanohi masks and use them to defeat Makuta who had polluted the minds of the animals of Mata Nui, known as Rahi, and put the Great Spirit Mata Nui to sleep. Tahu became the leader of the team.
In their first journeys throughout the island Onua gained five other masks aside from his mask of strength. They gave him the powers of underwater breathing, x-ray vision, super speed, shielding, and levitation. At the temple Kini Nui the six masks were combined into one golden mask that allowed him to use all of his mask powers at once.
The toa descended to the deep tunnels of the island where they faced shadow versions of themselves, created by the Makuta. They were victorious and reemerged and finished reverting the Rahi to normal.
The toa later faced the threat of the Bohrok swarms, mechanical bugs that functioned as suits for the Krata. The toa gathered one of each kind of Krata and used them to unlock and activate the exotoa, power suits of armor. They then used these suits to battle the Barahg twin queens. At the end of the battle they took off the armor to unite and use their combined power to imprison the Bahrag. The resulting energy burst threw them into pools of energized molten protodermis transforming them in to the toa nuva.
Onua became Onua nuva. His golden mask was turned into the Pakari nuva. It could no longer gave him the powers of underwater breathing, x-ray vision, super speed, shielding, and levitation, but his super strength was hugely increased and he could share that strength to allies nearby. His claws became chainsaws that he could place on his feet and use like roller skates. Onua nuva also had much greater earth control.
Shortly after the Bohrok Kal attempted to free the Bahrag. Tahu nuva was given the mask of time by the Turaga, who also cautioned him against its use. It gave him complete control of time. He used to defeat the Bohrak Kal by slowing time long enough for the other toa to stop them from freeing the Bahrag.