Ghouls (喰種, gūru, translates approximately to eater species) are a carnivorous and cannibalistic species that is only able to feed on humans and other ghouls. They are as close to humans as possible: They normally have the same physical appearance and intelligence as a human with the exception of diet, mentality and inner biology. If certain rare conditions are met, ghouls and humans may even be able to have offspring (see One-Eyed Ghoul), and a ghoul's organs can be successfully transplanted into a human. Besides water and coffee, a ghoul can only feed on humans and other ghouls. They are unable to digest any other type of food due to a particular enzyme their bodies produce. The structure of their tongues are also different from humans', making other foods taste disgusting and uncomfortable. While ghouls can't eat normal food, they are able to drink coffee. They are also able to drink plain water. If ghouls try to eat normal food, they will be struck by a powerful urge to vomit. When forced or forcing themselves to digest such food, it will degrade their physical condition. Ghouls don't need to eat in the short term like humans do.
Touka Kirishima describes this state of near-starvation as hell.
They can survive for one or two months just feeding on one body. However, some ghouls eat only for pleasure. An example would be Tsukiyama Shuu, who is fixed upon eating Kaneki Ken due to a bizarre curiosity as to how half-ghoul flesh would taste. When a ghoul enters an extreme state of hunger, they will suffer very painful headaches and lose all reason, causing them to become driven by instinct alone. They will feed on any available source of human meat to end this state, even that of close friends. Touka Kirishima describes this state of near-starvation as hell. Although ghouls can go up to two months without human flesh, some ghouls can feed on more than eleven people in just a few days, This is known as 'binge eating,' a habit sustained by Rize Kamishiro. Ghouls have high physical capability and produce kinetic energy in their muscles 4-7 than that of a human. They are able to send the average human flying if they strike with enough force and can penetrate a human's body with their bare hands. They are also able to jump several meters high. Under normal conditions, ghouls have a high regenerative ability: Small wounds and fractures heal in a matter of hours to a day, and even grave wounds heal after a few days, as long as the ghoul has adequate food supply. They also have a tougher body than most regular solid materials.
For example, if a ghoul were to be stabbed with a knife, the metal of the knife would bend. Ghouls' body wouldn't get injured easily and only more keen tougher materials can injure them. A strong enough force may also be able to break their tough body. Ghouls have keen senses. They can smell people or meat from afar and can tell apart humans and ghouls by their smell. Some ghouls have a heightened sense of hearing that even allows some ghouls to discern individual footsteps from far away. Ghouls seem to age at the same rate as humans, further allowing them to blend in. Ghouls have an "Rc factor" ten times higher than a human. If the average healthy human has about 200-500 Rc level, then the ghoul has about 1000-8000 Rc level. They possess an organ known as the kakuhou, from which Rc cells harden and break through the skin to form the kagune. The kagune is a hard, muscle-like protrusion described as their claws.
There are no known links as to where ghouls evolved or came from.
It can take the form of a pair of sharp wings or tentacle-like appendages, a tail, or a drill-like object, depending on the ghoul's materials and his or her own Rc type. It is possible for a ghoul to have develop another, usually armor-like, kagune as part of the mutation caused by eating another ghoul. Ghouls also have an identifying feature known as a Kakugan, an affliction manifesting in the eyes as red pupils surrounded by black sclera. A ghoul's kakugan can appear either by their own will, due to hunger or from using their kagune. Ghouls have a liking for human meat, but it is not uncommon for them to cannibalize one another. Ghoul meat is considered coarse and disgusting but it has the merits of being an alternative food source and increases a ghoul's Rc levels to the point of mutation, evolving their kagune's overall strength. Occasionally, cannibalistic ghouls gain through this mutation an armor-like kagune besides the predatory kagune that ghouls commonly possess, turning them into kakujas. Currently, the origin of these traces in ghouls is unknown. There are no known links as to where ghouls evolved or came from. Ghouls can be killed if forced to consume normal food, which will weaken their physical condition and possibly make them vulnerable to man-made objects such as guns, knifes, swords. Ghouls will die if they receive extremely critical or life-threatening injuries that will kill them before they have a chance to heal. It has also been said that a ghoul can be killed by decapitation but by what weapon or object is the mystery.
However some Ghouls are capable of surviving this as is the case of Noro who was able to re-attach his head back on even after it was cut off and sustaining damage that would kill a regular ghoul. Ghouls can live as hermits isolated and avoidant of society eyes or can attempt to assimilate with the humans. Living amongst humans is seen as "walking on a thread of rope" because of their biology and social records. If they are caught in ghoul activities or suspected to be a ghoul, investigators have the right to apprehend and kill them as they see fit. Ghouls that are identified are labeled can be hunted down like fugitive criminals. Because a ghoul doesn't require much due to their high physique and their diet of human meat, they can live adequately as vagabonds with little to no money, although such a life is generally as discomfortable as it might be for a human. Nonetheless, funds obtained from their societal jobs or careers are spared of the cost of food and could be spent on other necessities.
They can pretend to eat food in order to fool other people into believing they are human. However they must make themselves throw up soon enough afterwards, or they'll become sick. Because they can only consume human flesh, they are very territorial when it comes to "hunting grounds" on which it is appropriate to hunt humans without notice. Human consumption depends on the ghoul as some may prefer to be scavengers who only take from people who were recently deceased. Other ghouls may moderately hunt humans as carnivores with thoughts of appreciation for the lives they must consume, although there are ghouls who will indiscriminately devour as much as they can. Ghouls who indulge in excess have developed a superficial view on the value of life after consuming so many humans, much like how humans perceive livestock they grow and consume. A One-Eyed Ghoul is a human/ghoul hybrid. A Kakuja is a ghoul who has gained an armor-like kagune through repeated cannibalism.
The Quintessential Quintuplets (Japanese:, Hepburn: Go-Tōbun no Hanayome, lit. Japanese manga series written and illustrated by Negi Haruba. It was serialized in Kodansha's Weekly Shōnen Magazine from August 2017 to February 2020, with its chapters collected into fourteen tankōbon volumes. The series follows the daily life of a high school student Futaro Uesugi, who is hired as a private tutor for a group of identical quintuplets: Ichika, Nino, Miku, Yotsuba, and Itsuki Nakano. At the very beginning of the story, it is shown that the events are being told in a flashback, while an adult Futaro prepares to marry one of the Nakano Quintuplets whose identity is only revealed near the end of the series. The series is published in English by Kodansha USA under the Kodansha Comics imprint. The anime series is licensed in North America under a Crunchyroll-Funimation partnership. An anime television series adaptation produced by Tezuka Productions aired from January to March 2019 on TBS and other channels. The series is a commercial success, being the 5th best-selling manga in 2019, and the 3rd best-selling manga in the first half of 2020 in Japan. In 2019, the manga won the award for the shnen category at the 43rd annual Kodansha Manga Awards. High school student Futaro Uesugi is an academically gifted student that leads a difficult life-his mother has died, he has no friends, and on top of all that, his father has incurred a large amount of debt. An opportunity presents itself when the rich Nakano family transfers to his school.
Futaro is promptly hired as a highly paid tutor. However, much to Futaro's dismay, he discovers that his five charges-identical quintuplet sisters of varied personalities-have no interest in studying at all and have abysmal grades. Some of the quintuplets are against having Futaro, whom they view as a stranger, in their apartment, but Futaro's diligent tenacity gradually convinces those girls to accept him and to improve their grades. Throughout the series, Futaro develops special relationships with each of the quintuplets. Through a flashforward, it is revealed that he eventually marries one of them, but her true identity is only revealed near the end of the series. The idea of "a group of quintuplets falling in love with the same person" existed even before the serialization of Haruba's previous work, Karma of Purgatory (2014-2015), but was very simple at that time. The idea was denied by his editor-in-charge. A year after, after the end of Karma of Purgatory, he discussed with his editor-in-charge what to serialize next.