Kakuja

Kakujas (赫者, shining one ) are a transformed kind of ghoul that rarely appear by repeatedly cannibalizing ghouls. When a ward gets increased amount of ghouls, more instances of cannibalization occur because of turf wars or when "food" becomes scarce.

Sometimes, the transformation is incomplete, and such individuals are called Half-Kakujas.

Biology
It is said that through cannibalism, a ghoul absorbs Rc cells, and this uptake of Rc cells increases their concentration within a ghoul's body. If the concentration becomes high enough, it may trigger a mutation within the cells and lead to the formation of a new kagune.

A kakuja can evolve their armor kagune further by continuing to cannibalize their kind. For instance, while the One-Eyed Owl had a human-shape and size before its disappearance, it eventually developed into a much larger and monstrous form during its attack at Anteiku.

Powers
Apart from the predatory kagune ghouls commonly possess, a kakuja has a special kagune that clads the ghoul's body and functions like an armour. The kagune amplifies the kakuja's strength or diversifies his abilities, which makes a fight against one of them especially hard.

However, using a kakuja kagune is nearly impossible because most users tend to lose their minds while fighting with it. It is unknown why some ghouls are able to remain sane and others are not. One reason may be that all unstable/insane ghouls using kakuja are half/incomplete as full kakuja aren't observed to have any problems maintaining control.

It appears that a kakuja kagune can form a mask over the user's face if need be.