Takua was the very first Matoran built by the Great Beings. He was not only a test build to see if their nanotech workers would perform as expected, but a way to test early builds of GSR programming.
Headcanon that Takua's programming was granted administrator privileges to the GSR. The Great Beings wanted to make sure the automated systems would interact safely with an administrator before they tested things themselves. If their test subject was attacked or destroyed, well they could always build another.
Additional Headcanon that when the Great Beings were finished and dumped Takua in with the rest of the Av-Matoran they cleared his memory but forgot to remove the administrator privileges. This played an accidental role in the rest of the storyline.
This explains why only Takua could summon the Toa Mata or enter the Bohrok Nest unhindered. He still retained the privileges as Takanuva but couldn't bypass Karzahni's barrier because he too had overwright privileges on part of the GSR and could exclude anyone he wanted.
Had he gotten past the barrier with the rest of his friends, he would have been able to walk them down the 777 stairs without tripping any of the protection systems. Had he wanted to, he could have also walked straight into the Codrex without the key.
With his access to the GSR systems, he would have been able to walk into Mata Nui's brain if he knew the way. Likewise, if he had known how to code he could have rewritten the traits and personalities of others, not unlike a Makuta virus.
Had the Great Beings gone back to visit the GSR, Takua would have been able to see them despite the programming block placed on non-administrators to render them invisible.
*Great Beings in Metru Nui pre-Teridax Attack, Standing around Ta-Metru looking at various Matoran while 'unseen' by the locals.*
Great Being 1: "Hmmm, the project is progressing well enough, but how did they all gain sapience? We didn't program them for that!"
Great Being 2: "Someone must have interfered..."
Takua: *From Behind Them* "Oh hey, you guys must be tourists! I've never seen anyone like you before. What island are you from?"
Great Beings: *Incoherent Shrieking*
