Tokyo Ghoul is set in an alternate reality where ghouls, individuals who can only survive by eating human flesh, live among the normal humans in secret, hiding their true nature to evade pursuit from the authorities. Including enhanced speed, senses, and regenerative ability, a regular ghoul is several times stronger than a normal human, has a skin resistant to ordinary piercing weapons and has at least one special predatory organ called a "Kagune", which it can manifest and use as a weapon during combat. Another distinctive trait of ghouls is that when they are excited the color of their sclera in both eyes turns black and their irises red. In the case of a half-ghoul, only one of the eyes undergoes the transformation. A half-ghoul can either be born naturally as a ghoul and a human's offspring, or artificially created by transplanting some ghoul organs into a human. In both cases, a half-ghoul is usually much stronger than a pure-blood ghoul. There is also the case of half-humans, hybrids of ghouls and humans that can feed like normal humans and lack a Kagune while possessing enhanced abilities, but shortened lifespans. To hunt down the ghouls, several government-sponsored organizations around the world were created.
