Kagune

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 colours are varied in the anime to distinguish the Kagune of each individual); and flexible like the flow of water (Also called liquid muscle.), 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. A Kagune can be repeatedly hardened and softened at will by the ghoul.

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. Also it seems that the Kagune are voluntary muscles as ghouls can control them whenever they want. Kagune size depend on the Rc cells quality and quantity while the shape depend on the creativity and intellect of the user.

Rc Types
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 CCG in the creation of the Quinque and Q bullets.

Ukaku
An Ukaku Kagune (Japanese 羽赫, romanization ukaku, English 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 hugely enhanced speed. The kagune is lightweight and can be used to deliver high-speed attacks against an adversary, the primary method of attack is crystallising their kagune to deliver a high speed torrent of spike like projectiles, however whilst crystallised they are much stiffer and can't be used for short range combat. While the kagune is suited both for short-distance and long-distance attacks, short-range is considered their weakness. They are able to use their kagune as a shield and some users are shown to be able to shape them into sharp blades, reminiscent of a Koukaku, to aid in close quarters, many have shown to be able to increase the flexibility of their kagune for short range combat though this makes it ill suited for their distinctive long range attacks and some User can also shoot rc projectiles from their body not only from their kagune.

Altogether, ukaku-type ghouls have a high chance to end the battle after a short time. However, releasing the Rc cells extremely decreases stamina. Thus, ukaku-type users lack endurance and are at a disadvantage if the battle drags on for a long time.

Ukaku kagune can use their speed and mobility to shoot down a Bikaku-type user. However, a koukaku-type user can surprise an ukaku-type user by successfully guarding against the ukaku-type user's attacks, leaving the Ukaku vulnerable to counterattacks and exhausting the ukaku-type user in the long run.

Known Ukaku Ghouls are Kazuichi Banjou, Eto, Kaya Irimi, Ayato Kirishima, Hikari Kirishima, Touka Kirishima, Noyama, Ginshi Shirazu, Sumiharu Katou, Koharu Utsumi, Yoshimura, and Renji Yomo.

Koukaku
A Koukaku kagune (Japanese 甲赫, romanization kōkaku, English shell-red) is released below the shoulder blade. Due to its high density of Rc cell 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 kagunes and the kagune is hard 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, Arata Kirishima, Matsumae, Ikuma Momochi, Naki, Nutcracker, Nutcracker's Partner, Donato Porpora, Mirumo Tsukiyama,  Shuu Tsukiyama, and Kuki Urie.

Rinkaku
A Rinkaku kagune (Japanese 鱗赫, romanization rinkaku, English 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 that some of them could even survive the most critical damage done to them. Kaneki Ken, a rinkaku, has abnormal regenerative abilities as he inherited Rize's kagune. 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 more similar to liquids. However, this means that the binding force among the Rc cells must be 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.

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's 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's attack can disable a Rinkaku's regeneration.

Known Rinkaku Ghouls are Yuuri Akanuma, Asa, Asaki Fueguchi, Hinami Fueguchi, Rize Kamishiro, Ken Kaneki, Kie Muramatsu, Nico, Yakumo Oomori, Kanae von Rosewald, Karao Saeki, Kurona Yasuhisa, Nashiro Yasuhisa, and Saiko Yonebayashi.

Bikaku
A Bikaku kagune (Japanese 尾赫, romanization bikaku, English 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."

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 investigators.

Known Bikaku Ghouls are Big Madam, the Bin Brothers, Cain, Grave Robber, Akashi Kobayashi, Enji Koma, Matasaka Kamishiro, Miza, Tooru Mutsuki, Nishiki Nishio, Uruka Minami, and Nutcracker.

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 Eto, Ken Kaneki, Arata Kirishima, Yakumo Oomori, Seidou Takizawa, and Yoshimura.

Chimera
When Ghouls with different Rc types have children, there is a small chance that they will inherit abilities from both parents. This trait appears to be extremely rare, with only two known examples appearing in the series.

Known Chimera Ghouls are Hinami Fueguchi and Nutcracker.

Detachment
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. Thus far, two distinct uses have been observed: Walls and Traps.

A detached 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. Thus far, the only example is the Koukaku Ghoul, Matsumae.

A detached 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 whatever set them all. It appears to be possible to set more than a half-dozen traps at a time, though the exact limitation is unknown. The only example thus far is the Chimera Ghoul Nutcracker.

The One-Eyed Ghoul Eto demonstrates the ability to detach pieces of her kagune, using them to manipulate and restrain targets. It is possible that this is a variant of the Kagune Wall, though the exact details are unknown at this time.

Trivia

 * 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.
 * Grave Robber's bikaku kagune drains their stamina significantly, to the point they prefer 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.
 * Yoshimura's ukaku kagune takes the form of a long blade, resembling a koukaku-type kagune and functioning just as well in close combat.