Takanuva is the Toa of Light, the Seventh Toa and the conqueror of evil. He is, however, the least experienced of all the Toa considering he was a Matoran originally. He used to be Takua the Chronicler, a Ta-Matoran who often shirked his work and never felt comfortable where he was. Because he was born to be a Toa.
After his friend Jaller was killed by the Rahkshi Turahk, Takua realized who he was and found the Seventh Toa: himself. He was then changed into Takanuva, and defeated the lone Turahk. He then solemnly brought his best friend, Jaller, down the steps of the Kini-Nui. Vakama talked to him and he was convinced to not let Jaller's sacrifice be in vain. Using plans which were already in his head, probably unlocked by the discovery of the Mask of Light, the Toa constructed a vehicle called the Ussanui out of Rahkshi parts. Using Kraata as the power so they would direct Takanuva to his lair, Takanuva flew down into the darkness.
He crashed into the wall, back flipping before it hit an was startled to see that Hahli had stowed away in a small wedge in the vehicle. He accepted that and stepped in Mangaia, Makuta's lair. Letting the Kraata go into the darkness, he called to Makuta and told Hahli to summon the Turaga and Toa. She hurried back while Takanuva confronted Makuta. Makuta challenged Takanuva to a simple game of Kolhii. He agreed, and when the Turaga and Toa arrived they were in a fierce match of dark and light energy. But Takanuva had one thing Makuta didn't have: experience. As the Chronicler, he was one of Ta-Koro's Kolhii players. Using a move he had tried once before but never worked, he caught Makuta's blast, converted it into light energy and swung it at him in full force. Makuta was blasted back into the wall.
Then Makuta emerged, angry and approached Takanuva ready to knock him down. However, by something Makuta said Takanuva got an idea. He literally jumped on Makuta and forcefully took his mask off, switching their masks! Makuta rolled back and took both of them into a pool of energized Protodermis.
The pool lit up and a new being emerged: Takutanuva. The light part of this being had 'enlightened' Makuta. Now both were all for opening the doorway to Metru Nui, City of Legends. They lifted it high, and the Turaga and Toa went through hurriedly. But as Hahli passed through it with Jaller's Kanohi, Takutanuva stopped them and Makuta gave his own life force to revive Jaller. Takutanuva could not hold it any longer. The door fell and his Kanohi slid out of the doorway.
The Turaga approached the balcony in awe of what was before them: their old island home, Metru Nui. Vakama proclaimed the three virtues, placing Jaller on the Duty symbol of a large symbol on the balcony, Hahli on the Unity side and Takanuva's mask on the Destiny symbol. Light lit up the balcony, and Takanuva reappeared.