The Kanohi Akaku Nuva was a type of Kanohi Nuva mask with the power of X-Ray Vision. It was a more powerful version of the Akaku which could only be used by Toa Nuva. The Akaku Nuva allowed its user to see through both opaque objects and illusions. As with all Kanohi Nuva, the user could also share this ability with nearby allies.
Notes
The Great Mask of X-Ray Vision. It allowed the user and those close by to see through walls and discover that which was concealed by physical means or illusion.3
The Akaku Nuva was the Great Mask of X-Ray Vision. It allowed its user to see through walls and illusions.4
The Akaku Nuva was the more powerful Mask of X-ray Vision worn by Kopaka Nuva. Like all Kanohi Nuva masks, its power could be shared by the user with those in close proximity.5
If Kopaka shared the power of his Akaku Nuva, the other being wouldn't be able to use the telescoping feature. This is because the telescope was an add-on for the mask rather than part of the mask's power.6