Kakugan

A kakugan (赫眼, red eye) denotes a ghoul's eye where the iris turns red, and the sclera black with red veins across the eye and into the skin around the eye. A ghoul could activate their kakugan at their own will, or when they are hungry, excited or using their Kagune. A Kakugan is the influence of activated rc cells.

A normal Ghoul possesses two kakugans and activate together. If a person possesses one kakugan they are known as a One Eyed Ghoul'''. A new type of Ghoul/Human hybrid called a Quinx '''possess only one kakugan like a one-eyed ghoul, but their sclera is grey instead of black. It is unknown if the kakugan serves any supplemental purpose.