Cannibalism is the act or practice of species eating the flesh or internal organs of their kind. In the story, scenes of ghouls eating ghouls and humans eating humans pass regularly as the narrative continues.
Strictly speaking, one-eyed ghouls(Artifical) always have to cannibalize since they are forced to eat human or ghoul meat. In their case, however, only eating ghoul meat is typically treated as cannibalism.
Ghoul meat tastes disgusting to ghouls, but in contrast to other non-human nutrition, they are able to digest it. Continued cannibalization may trigger a mutation in Rc cells, resulting in turning them into kakujas.
Effects on Ghouls
If a ghoul engages in cannibalism, it absorbs the Rc cells of the cannibalized ghoul, thus increasing the concentration of Rc cells within the ghoul consuming them. If repeated often enough, there is a slight chance that this will trigger a mutation in the Rc cells of the ghoul and lead to the formation of a new armor-like kagune. Individuals with such a kagune are called kakujas. This armor-like kagune increases a ghoul's power substantially.
However, a ghoul that uses the powers obtained from cannibalism may go insane. It is unknown why some ghouls are able to remain sane and others are not, although it may just be a matter of mental resilience.