One-eyed ghoul

A one-eyed ghoul (隻眼の喰種 Sekigan no Gūru) is a human-ghoul hybrid who possesses a ghoul's abilities. Most ghouls treat their existence as an urban legend or have never heard of their existence at all.

Characteristics
One-eyed ghouls earn their name from the single kakugan they possess, in contrast to normal ghouls. In all other ways, they appear to have no obvious differences from an ordinary ghoul. Some individuals are noted to have a unique scent that combines traits of a human and a ghoul, identifying them as different and often considered "enticing" by certain ghouls. Ken Kaneki has been shown to smell like a ghoul by some individuals whereas some cannot tell the difference, and Eto has been shown to smell like a human so far. It is unknown whether all hybrids have this trait. Their flesh and blood is also noted to be particularly delicious, making them a potential target for cannibalism. Dr. Shiba claims that the more half-ghouls and Quinx get hurt, the more their basic abilities will increase.

Rumors state that hybrids are more powerful than ordinary ghouls due to hybrid vigor, though it has not been further elaborated on. All specimens (except Furuta and Nashiro) have demonstrated radical evolution of their abilities and developed into, sometimes partial, kakujas within a short period of time. Physically, their bodies are identical to that of a ghoul with the same resistance to harm and ability to use a kagune. Like normal ghouls, they are only able to consume meat of human or ghoul origin, as well as coffee and water; Eto has been shown consuming human food, but it is unknown if she can eat it without any adverse effects at this time. As such, they are inherently a cannibalistic organism. Hybrids come into existence through two methods, either normally born as a result of the union between a male ghoul and a female human, or through transplanting a kakuhou into a human host.

Pregnancy
Naturally-born hybrids born with ghoul abilities are extremely rare. 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 unless the mother engages in cannibalism.
 * If the mother is a ghoul, the mother's body will mistake the child for food and reabsorb it.

Half-Humans
Should a child be conceived from a ghoul father and a human mother, there are mostly likely to be born as half-humans and are far more common. They possess enhanced physical abilities but not the traits from their partial ghoul descent (i.e, lacking of kagune, kakugan).

Kakuhou Transplant
The primary method of creating one-eyed ghouls is through transplanting a kakuhou into a human recipient, an exceptionally high-risk procedure. In the rare event that the operation is successful, the human patient develops into an artificial hybrid with all the abilities of a normal ghoul. This procedure was pioneered by Dr. Akihiro Kanou, with the first successful patient believed to be Ken Kaneki.

Kanou, while experimenting with Takizawa, compared his surgery with grafting, a horticultural technique where the tissue of two trees are combined to help them both grow stronger. According to him, the transplant gives the subject a stronger, much more durable body and partially reduces the their need to feed and replenish, indicating that artificial one-eyed ghouls can survive longer without food compared to normal ghouls. However, he confirms that the process does shorten the subject's lifespan.

Currently, it is unknown what side-effects the process causes on a half-human subject, considering that their parentage already gives them a shortened lifespan.

Kurona Yasuhisa is a strange case for an artificial one-eyed ghoul. After absorbing her sister into her body, she developed two kakugan in place of one. It is unknown as to why she developed two kakugan after absorbing her sister, who was also a one-eyed ghoul.

Quinx
After examining Dr. Kanou's surgery on Ken Kaneki, the CCG created an experimental squad consisting of humans with ghoul capabilities through implementing a kakuhou covered by quinque steel layers. While the Quinx are not considered as normal half-ghouls due to their lower Rc cell levels and the ability to eat human food, they are made from the concepts of Dr. Kanou's half-ghoul experiments.

Natural

 * Eto

Artificial
Kanou has created two series of artificial ghouls: The "Eater-series" artificial ghouls created from "Binge Eater" Rize Kamishiro's kakuhou and the "Owl-series" artificial ghouls produced from "Owl" Yoshimura's kakuhou.

Rize-based

 * Ken Kaneki/Haise Sasaki (K-Eater)
 * Kurona Yasuhisa (B-Eater, Floppy)
 * (W-Eater)
 * Souta Washuu-Furuta

Yoshimura-based

 * Seidou Takizawa (T-Owl)
 * Koutarou Amon (Floppy)

Trivia

 * Itori and Uta share rumors of another one-eyed ghoul with Kaneki, advising him to not seek out this being because of the danger involved. It is likely they were referring to the One-Eyed Owl.
 * Eto is the only confirmed case of a natural-born half-ghoul.
 * Fujishige Iba once mentioned to his subordinates that there was a scientist that wanted to experiment with hybridization, but his research was deemed unethical and shut down.
 * One-eyed ghouls are stated to be more powerful than normal ghouls as a result of heterosis, also called "hybrid vigor." This phenomenon involves the offspring of two different breeds or species inheriting superior traits from its parent and is frequently used in agriculture and animal husbandry.
 * Akihiro Kanou refers to the failures from his experiments as floppies, though it unclear what difference there may be between a floppy and successful artificial one-eyed ghouls. However, it could be that they are not as strong as he hoped. This was shown when he compared the Yasuhisa twins to Kaneki he mentioned that they were not as strong as him thus they are failures, thus floppies.
 * According to Eto, about a hundred years prior to the current timeline and events in the manga series, there existed a one-eyed ghoul so powerful that the ghoul's appearance led to the foundation of the CCG's predecessor organization.
 * Kurona Yasuhisa is the only one-eyed ghoul who has two kakugan.