A kagune (赫子, red child) is a ghoul's predatory organ and functions as their weapon and claws. It is usually as red as blood (the colors are varied in the anime to distinguish the kagune of each individual), flexible like the flow of water, but firm and sturdy. When released, a ghoul's physique is strengthened, they are more resilient, and their mobility heightens. A kagune is composed of Rc cells, which flow just like blood, can become as solid as teeth and can be described as "liquid muscles." The Rc cells are released from a kakuhou piercing the skin, and the released Rc cells form the kagune. The kagune are voluntary muscles as ghouls can control them whenever they want and repeatedly harden and soften them at will. Kagune size depend on the Rc cells' quality and quantity while the shape depends on the creativity and intellect of the user.
Although a ghoul's healing ability is high, the healing of wounds tends to be delayed if the wounds are inflicted by a kagune. It is also evident that in order to counter a kagune in battle, one must also have a kagune, if not, at least something in relation to a kagune. Hence, ghoul investigators use kagune-based quinque as a tactical means to battle against ghouls.
Research conducted by the CCG Laboratory Division resulted in identifying three stages of kagune formation. At their current knowledge, the stages are the same for every ghoul capable of manifesting kagune.
At the point base of the kagune where the Rc cells erupt from the kakuhou, the erupted Rc cells will form bonds with each other. They will organize themselves in the structure best fit for their Rc type in a repeated web. This repeated action of the cells will occur instantaneously and lead to the next stage.
The bonded Rc cells will retain the resulted form for a fixed length of time. The basic shape of the kagune is seen at this stage. During this time, the defensive and offensive capabilities and weaknesses will take on their respective properties to the ghoul's Rc type. The manifested kagune's appearance is usually hereditary, taking on the shape and characteristics of their genetic predecessors, additionally, kagune size also depends on the Rc cells' quality and quantity while the shape depends on the creativity and intellect of the user. In relation to this stage is the user's manual control of the kagune's movement and actions, which can include crystallization and increase in length, dexterity, sharpness, and concentration.
After time has elapsed, the bonds between the cells begin to break apart. At this point, the kagune loses its intactness or solidity and deteriorates.
The kagune's appearance and the place of emergence on the body depend on the Rc type of the ghoul. There are four different Rc types: ukaku, koukaku, rinkaku, and bikaku. As a guideline, each type can characteristically subdue another type, although it may be different for two specific opponents. Each Rc type has a set of strengths and weaknesses, each one unique to its type. These are exploited by the CCG in the creation of the quinque and Q bullets.
An ukaku kagune (羽赫, ukaku, "feather-red") is spread out like feathers and is released from the shoulder area, it specializes in high speed attacks, most of the users seeming to have highly enhanced speed. The kagune is lightweight and can be used to deliver high-speed attacks against an adversary, the primary method of attack is crystallizing their kagune to deliver a high speed torrent of spike-like projectiles, however whilst crystallized they are much stiffer and cannot be used for short range combat; at least one ukaku-type can generate powerful lightning-like bolts, a possible rare ability. While the kagune is suited both for short-distance and long-distance attacks, short-range is considered their weakness. They may use their kagune as a shield and several are capable of shaping them into sharp blades reminiscent of a koukaku to aid in close quarters. Many ukaku-types are able to increase the flexibility of their kagune for short-range combat, though this makes it ill-suited for their distinctive long-range attacks.
Altogether ukaku-type ghouls have a high chance of ending a battle quickly as releasing Rc cells depletes stamina. Thus, ukaku-type users lack endurance and are at a disadvantage if the battle drags on for a long time. Ukaku-type users can use their speed and mobility to shoot down bikaku-type users from afar. However, a koukaku-type user can suppress an ukaku-type user by successfully guarding against the ukaku-type user's attacks, leaving them vulnerable to counterattacks and exhausting the ukaku-type user in the long run.
Known ukaku ghouls are: Shinsanpei Aura, Kazuichi Banjou, Fei, Shousei Idera, Kaya Irimi, Sumiharu Katou, Ayato Kirishima, Hikari Kirishima, Touka Kirishima, Kurei, Noyama, Ruchi, Shikorae, Ginshi Shirazu, Seidou Takizawa, Koutarou Amon, Koharu Utsumi, Renji Yomo, Yoshimura, and Eto Yoshimura.
A koukaku kagune (甲赫, kōkaku, "shell-red") is released below the shoulder blade. Due to its high density of Rc cells, it is heavy and extremely robust, giving it the greatest sturdiness and making them very well suited for defense. Normally, they are generally shaped into armors or shields, but on the offense, they can be shaped like melee weapons such as drills, hammers, blades, and swords.
Due to its high weight, a koukaku's speed is inferior to all other Rc types and the kagune is difficult to wield.
A koukaku can fend off an ukaku onslaught using its guarding capabilities. However, a rinkaku kagune can deliver severe strikes against the slow koukaku, breaking their kagune and breaching their defenses.
Known koukaku ghouls are: Hinami Fueguchi, Ryouko Fueguchi, Ching-Li Hsiao, Arata Kirishima, Mairo, Matsumae, Ikuma Momochi, Naki, Nutcracker, Nutcracker's partner, Donato Porpora, Rou, Shikorae, Tanaka, Mirumo Tsukiyama, Shuu Tsukiyama, and Kuki Urie.
A rinkaku kagune (鱗赫, rinkaku, "scale-red") has an appearance similar to scaled tentacles and is released at the back around the waist. A rinkaku wielder has powerful regenerative abilities and some could even survive the most critical of damage. Its peculiar appearance and structure yield a superior striking power and they excel in brute strength. Some rinkaku users are able to manipulate the shape of their kagune, such as changing its usual tentacle form into swords or claws.
This type's regenerative power is a result of the Rc cells easily binding together. Their Rc cells are similar to liquid. However, this means that the binding force among the Rc cells are weak, therefore making the kagune very soft and easy to break. But because their Rc cells bind so easily, some rinkaku can bind their multiple tentacle-like kagune together to make a larger, stronger kagune. So far the number of tentacles that rinkaku users can create are from one to eight tentacles.
A rinkaku kagune can deliver severe strikes against the slow koukaku, penetrating the kagune and breaching the koukaku's defenses. However, a rinkaku has serious problems fighting against the balanced bikaku kagune: A bikaku has comprehensively high power, allowing them to fight against the brute-force rinkaku, and the rinkaku kagune softness makes it comparatively easy for the bikaku to cut the kagune off. This disarms a rinkaku no matter how much strength it may possess, leaving the rinkaku at a disadvantage on the defensive. It has been shown that in some cases, a bikaku attack can disable a rinkaku's regeneration.
Known rinkaku ghouls are: Yuuri Akanuma, Asa, Asaki Fueguchi, Hinami Fueguchi, Nimura Furuta, Hajime Hazuki, Hooguro, Rize Kamishiro, Ken Kaneki, Kinko, Kie Muramatsu, Yakumo Oomori, Rio, Rio's brother, Wobbegong, Kanae von Rosewald, Karao Saeki, Kurona Yasuhisa, Mayuzumi, Nashiro Yasuhisa, and Saiko Yonebayashi.
A bikaku kagune (尾赫, bikaku, "tail-red") typically has a tail-like appearance and is released around the tail-bone/coccyx. It is good for medium-distance attacks and has decent offense, defense, and speed. Thus, they have no notable strengths or weaknesses like the kagune based on other Rc types, meaning the kagune itself is treated as a surprise "trump card." The number of tails a bikaku user can create is usally one, but some can create more.
A bikaku has better speed and durability against the brute-force, breakable rinkaku, allowing them to cut off the rinkaku's kagune. However, a bikaku will be overwhelmed by the faster ukaku-user and will lose against the ukaku's long-range attacks.
The balanced characteristics makes the kagune a preferred quinque type for inexperienced investigators.
Known bikaku ghouls are: Big Madam, the Bin Brothers, Cain, Demon Yamada, Touma Higemaru, Matasaka Kamishiro, Akashi Kobayashi, Enji Koma, Uruka Minami, Miza Kusakari, Tooru Mutsuki, Nishiki Nishio, Noro, Nutcracker, Shikorae, and Yumitsu Tomoe.
In some cases, a ghoul's kagune can possess several unique abilities. While the kagune's basic structure itself is quite simple, the occurrences concurrent with these phenomena are unexplained, however they have been accredited to highly concentrated amounts of Rc cells.
The kagune while in use may be surrounded by a lightning-like aura, capable of generating electricity that can be utilized in an offensive and destructive manner. This is not a learned characteristic, but is hereditary, originating from the kakuhou. Note this ability may be passed onto a quinque, shown by Narukami and T-Human. This ability has only been shown in ukaku type ghouls.
Thus far, this has only been demonstrated by Tatara in kakuja form, however, the mutated Rc cells were able to generate heat, as well as flames reaching 4000 degrees Celsius.
In both an ukaku and rinkaku ghoul this skill has been present, suggesting it may be an ability all Rc types are capable of. The wounded may be healed from injuries such as large fatal wounds to needing whole bones replaced. Whether they are another ghoul, human (albeit with added complications involving increased Rc factors), or the owner of the healing kagune, healing can be achieved within varying time parameters. Unlike electrokinesis, healing is not exclusively hereditary but can be learned like a skill which can be improved over time with experience, an example being Nico's experience healing humans, describing it as a "trick." Only Kazuichi Banjou and Nico have exhibited this ability.
This ability to mimic the appearance of others has only been shown by Uta , indicating its uniqueness. The extent with which it can be achieved is far enough to fool even those familiar with the individual being mimicked. This includes creating detailed facial features and body structures to be realistic enough to function much like the real thing.
- Main article: Kakuja
When ghouls repeatedly cannibalize other ghouls, they (rarely) develop an abnormal kagune apart from the common predatory kagune. This kagune typically takes an armor-like shape, and ghouls with such a kagune are called Kakujas.
This abnormal transformation kagune also takes after the Rc types.
Known kakuja ghouls are: Ken Kaneki, Arata Kirishima, Yakumo Oomori, Seidou Takizawa, Kurona Yasuhisa, Underground King, Tatara, Yoshimura, Yan, Koutarou Amon, Noro, Eto Yoshimura, Roma Hoito, Uta, Rize Kamishiro, Daikichi Washuu, Yoshiu Washuu, Tsuneyoshi Washuu, Yoshitoki Washuu, Matsuri Washuu and Kichimura Washuu.
- Main article: Chimera kagune
When ghouls with different Rc types have children, there is a small chance they will inherit abilities from both parents and be born with a chimera kagune. This trait appears to be extremely rare, with only three known examples appearing in the series.
Though the method has still not been explained, some ghouls possess a rare ability to detach part of their kagune. This detached piece maintains its traits for some time, and continues to function separate from the main body. Detachment can be used in several ways:
- kagune wall buries into the ground, and sprouts like a thorn bush or other organic barrier. It extends itself to fill the entire area, making passage impossible.
- kagune trap can be buried within any surface, and coils up on itself. These traps will lie in wait until nearby movement triggers them, bursting from their hiding place to impale what has set them off. It appears to be possible to set more than a half-dozen traps at a time, though the exact limitation is unknown.
- kagune signal is able to transmit data similar to a distress signal. How the information is transferred as well as received is unknown, but a small piece of kagune can reveal the owner's location. It has only been shown to work one-way so far.
It is possible for ghouls to use their detached kagune in more destructive and offensive ways. For instance, Kurona Yasuhisa detaches her kagune and wields it similarly to a quinque. In comparison, Koutarou Amon uses the kagune from his arm to complete the form of his damaged quinque, Doujima 1/2. Tooru Mutsuki, like Kurona, uses his like a quinque and applies his knife-throwing skills, he shapes them into knives to use them as such. On the other hand, Eto and Donato Porpora have demonstrated the ability to use the detached pieces of their kagune to manipulate and restrain targets.
- While the abilities of a ghoul's kagune can be primarily inferred based upon their Rc type, several ghouls' kagune differ in appearance and/or function from what their Rc type would normally imply.
- Yumitsu Tomoe's bikaku kagune drains her stamina significantly, to the point she prefers not to use it in battle.
- Ayato can use his ukaku kagune for long periods of time with little drain in his stamina. He also excels in close-quarters combat, despite those of the ukaku-type typically being better-versed in ranged combat. Both him and his sister's kagune are unusually flexible for an ukaku, being well suited for short range combat and defense, as well as the long range attacks ukaku-type ghouls specialize in.
- Yoshimura's ukaku kagune takes the form of a long blade, resembling a koukaku-type kagune and functioning just as well in close combat.
- During the Auction Mopping-up Operation, Matsumae sprouts hers koukaku into several versatile threads much like a rinkaku's to carry Kanae von Rosewald away.