Avohkii

Before Metru Nui Storyline
The great Avohkii Mask of Light was forged in Artahka. The Brotherhood of Makuta feared it could be used against them,so they took it from Artahka. Later,when the Toa Hagah rebeled,taking the mask with them. Later when they were all Rahaga,they hid it in the Great Temple.

Metru Nui Storyline
When the Toa Hordika met up with the Rahaga later,the Rahaga told them they must retieve the six Makoki Stones and use them to open the chamber in which it is hidden. But when the Toa were about to retieve it,a group of Visorak attacked them. Durring the battle, Onewa had enceased the mask in stone to protect it.The Toa took it to Mata Nui with them, and Vakama decorated the stone-enceased mask to look like an ancient totem.

Mata Nui Storyline
Vakama hid it in a volcano in which a 1000 years later, the Chronicler, Takua, found the totem.After accidentally dropping it in some lava,a Great Kanohi Mask floated to the surface! Nokama used her Mask of Translation to read text on it and it foretold it was to be worn by a 7th toa! Takua and his best friend Jaller, went to find the Toa of Light. However Makuta knew too,and sent his "sons", Rahkshi, to find the 7th Toa first. After many Rahkshi encounters,the two Matoran made all the way to Kini Nui.All 6 Rahkshi attacked the Matoran, only to be saved by the Toa Nuva. The Toa had beat all but one, Turahk, who kills Jaller.Realizing he's the 7th Toa, Takua puts on the mask.He turned into Takanuva and the next day he went to Makuta's lair. He fought Makuta and they both fell in some Energized Protodermis,and came out as Takutanuva. Takutanuva resurected Jaller,but he was then crushed under a huge gate out. Using Jaller, Hahli, and the recovered Mask, Takanuva is also resurected.

Powers
It has been said to be the opposite of the Kraahkan.