One-eyed ghoul

A one-eyed ghoul (隻眼の喰種, sekigan no gūru) is a human-ghoul-hybrid. Most ghouls treat their existence as an urban legend or have never heard of their existence at all.

Characteristics
Hybrids are labeled one-eyed ghouls because they only develop one Kakugan, in contrast to normal ghouls who develop Kakugan in both eyes.

Due to hybrid vigour, one-eyed ghouls are said to become much more powerful than normal ghouls.

Due to their hybrid nature, one-eyed ghouls are limited to food that both humans and ghoul can stomach, so they have to feed off humans and ghouls.

Pregnancy
Naturally-born hybrids are rare, if not impossible. The chance of pregnancy is low, and even if the mother becomes pregnant, the child normally dies during pregnancy: If the mother is a human, the child will not get necessary nutrients and will starve to death. If the mother is a ghoul, the mother's body will mistake the child for food and reabsorb it. However, there are rumours that a naturally-born one-eyed ghoul exists.

Specimen

 * Ken Kaneki (artificial)

According to rumours, there exists another one-eyed ghoul. Itori mentioned the witness reports were preposterous. This one-eyed ghoul seems to practice cannibalism due to his vigorous appetite. Uta advised Ken Kaneki not to search for him, because he never heard happy stories about the one-eyed ghoul.

Kureo Mado was searching for "One-Eye" to take revenge.