Their strength are usually represented by their number of tails. They are highly intelligent creatures that use what is known as Fox Senjutsu instead of relying on physical prowess. They are capable of feats that are beyond human understanding and possess incredible resistant to elements of this world. It is in their nature to come and go as they please, making them a difficult partner to work with.
Their come in all sizes and colors, but all of them share one similar trait, the ghostly flame that burns on the tip(s) of their tail(s). They are often worshiped as guardians and deities by the people.
Known Demon Foxes
Unnamed fox messenger, a tiny fox about the size of a small house cat with a coat of orange fur, and a short bushy tail. It posses the ability to travel freely between the human realm and the realm of Yōko.
Ichigo (一護) Its name is a pun on the Japanese word for "Strawberry". Gyururu's favorite Yōko. It's about the same size as a regular adult fox with a coat of red fur, and a long fluffy tail. It can't speak, but appears to enjoy accompanying Gyururu, unlike the other foxes.
Fuki (二鬼) Its name is a pun on the Japanese word for "Butterbur". A fierce fox about as large an adult tiger. It's coat is mostly blue, with a white underside, black pointy ears that point forward like a pair of horns, and 2 long bushy tails with white tips. It doesn't seem to understand human language, as it rarely follows Gyururu's orders.
Mikan (三柑) Its name is a pun on the Japanese word for "Tangerine". The cutest among the Yōko, Mikan is about the size of small dog with a coat of orange fur, a big pink ribbon on the back of her head, and 3 long fluffy tails. She has a cute high-pitched voice that maybe annoying to some, and enjoys being carried around in Gyururu's arms.
Shio (四御) Its name is a pun on the Japanese word for "Salt". Shio has a stern personality, and dislike fooling around, making it hard for it to possess Gyururu unless she is very serious. It is about the size of a large dog, with white fur, and 4 slender tails. It also wears a Shimenawa (Sacred Ropes) around its chest that is tied to his back, with a large golden bell on each end of the rope.
Goya (五夜) Its name is a pun on the Japanese word for "Bitter Gourd". The most unfriendly of the bunch. It has a long slender body that is covered in jet black fur, with a long slender tail that splits into 5 at the tip. It is about the size of a dog, but the length of its body allows it to coil around a person from head to toe. Goya is sarcastic in nature.
Mugi (六衣) Its name is a pun on the Japanese word for "Wheat". Adoring Sensatsu no Gyururu's beauty, Mugi often transform herself into a beautiful young lady with long wavy golden brown hair, wearing a thin light-colored Yukata. In her fox form, she is covered by a thick coat of golden brown fur, with 6 fluffy tails that looks extremely comfortable.
Nashi (七矢) Its name is a pun on the Japanese word for "Pear". Nashi is a slender fox with silver fur, and 7 tails that flow behind it like trails of smoke. It is quick on its feet, and is rarely seen standing in one place for too long.
Hachimitsu (八密) Its name is a pun on the Japanese word for "Honey". Hachi, as it is nicknamed, is a big fox with a round body that resembles a brown bear's. It has short brown fur and 8 short bushy tails which spreads out like a blossoming flower. It can speak, but rarely does due to its extremely shy personality.
Kuri (九里) Its name is a pun on the Japanese word for "Chestnut". A big lazy fox that is a big as a bus. Its fur is chestnut brown in color, with a bit of white on the tip of its ears, its toes and each of its 9 slender tails. Usually refusing to budge from the spot where he was summoned, it will go to great lengths to stay and protect his spot. Due to its lazy nature, it usually starts a sentence with a "Fw-aaaaaah" as it yawns before speaking. Several years ago, it was just a messenger fox the size of a small dog with one tail, under a different name. Kuri has never forgotten the time it had to deliver a birthday cake to Uematsu Tomi, as a favor for Sensatsu no Gyururu.
Hyakubi (百尾) Her name literally means "Hundred Tails", the 1st Yōko created by Senbi. Also known as the mother of all Yōko, she gave birth to all the other Yōko in existence. She has a coat of pure white fur and long slender tails that number in the hundreds. She is usually loving and nurturing, but can be extremely fierce when her children is in danger or hurt, and can even summon herself to the human realm during such occasion. She has the ability to change her size from being the size of a horse to being as big as a Bijuu.
Senbi no Yōko (千尾の妖狐, Demon Fox of a Thousand Tails), an ancient fox-like creature that is practically a God. It has a coat of pearl-white fur that shines in the colors of the rainbow, with its tails usually merged into one thick mass that resembles the tail of Shukaku, the Ichibi. It created the realm in which all demon foxes resides in, and feeds on the souls that accidentally wandered into its realm. It is capable of changing its size, possesses clairvoyant, can travel freely between realms, create physical clones of itself by shedding its fur, create life, and even recreate itself from nothing. It is impossible for a human to summon the Senbi.
Fox Senjutsu (狐仙術, Kitsune Senjutsu), are techniques that can only be performed by the Demon Foxes or those who can enter a form called Fox Mode as they require Demonic Chakra, a mixture of Demonic Energy (妖気, Yōki) and chakra. These techniques cannot be copied by the Sharingan. Below is a list of known techniques;
Fox Fire (狐火, Kitsunebi), the most common Senjutsu used by the Yōko, manifests as an inconspicuous ball of blue flames. Unlike natural fire, it produces no heat, does not physically burn anything, leaving one to wonder does it even exist since it is not effected by water or oxygen either. Upon direct, unprotected contact with a person or being however it will latch onto their chakra, and will continue to consume it until the victim has not a speck left. To some extent Fox fire has ability to do this to chakra-infused objects as well, though it can not completely deprive them of it lest it strikes near enough to the source of it.
Typically the more chakra the victim has, the bigger the flames can become, so being struck by them can be particularly lethal to people with a lot of it such as Jinchūriki. This does not mean it is a guaranteed death sentence however, for even if one does take a clean hit there are still ways to survive, such as severing the struck area or cutting off chakra flow there to starve out the flame.
Ethereal Form (幽体化, Yūtaika), a Senjutsu that enables the user to become ethereal by cloaking them with Demonic Chakra. This not only makes them immune to physical attacks, Ninjutsu, and lets them pass right through barriers and physical objects, but also makes them invisible to the naked eye. This technique does not prevent those with Doujutsu that can visually see chakra, and those who can sense chakra from locating the user.
Ethereal Hands (幽手, Yūte), a Senjutsu that creates see-through arms that stretch out of the users back, as if extra limbs. Numbering between 2 and 50 and capable of stretching from 2 up to 15 meters, depending on the skill of the user, the lack of any joints in the fingers grants the arms snake-like movements easily surpassing most human limitations. In their base state the arms are incorporeal, simply passing through any solid, non-spiritual objects harmlessly, but by raising their Demonic Chakra concentration the user may turn them solid. With sufficiently high level of control the user may even for example reach through a wall, only focusing Demonic Chakra to the hand after, allowing them to grab something on the other side, although they can not pull it through without violence as the grabbed object will still remain solid. While focused attacks may disperse the arms, as long as the user has the Demonic Chakra to spare they can be reformed at will, making them essentially impossible to get rid of besides incapacitating or exhausting the user themselves.
Despite it all however, the individual arms are no stronger than an average non-shinobi human, requiring the user to merge a multitude of arms together should they wish to physically restrain an opponent much less attempt lifting something particularly heavy. Additionally, manipulating a large number of arms places great strain on the mind due to the focus required, so prolonged usage may tire out even a fairly skilled user even if they didn't use up all their energy.
Explosive Curse (爆裂の呪縛, Bakuretsu no Jubaku), a Senjutsu capable of shattering anything tagged by the user with explosive force. The technique is applied by physically touching an object with the hand, which leaves a marking in the shape of the kanji "爆" (Baku, explode) on the surface of the object. Once tagged, the marking(s) can be triggered either individually by focusing on a specific one and chanting 'Baku', or exerting greater focus and chanting 'Bakuha' to detonate all of them at once indiscriminately. Regardless of the characteristic of the object, the technique will cause an explosion of shock waves and send debris flying in all directions. The mass of the object greatly influence the force of the explosion. The technique can only affect roughly the mass of an average adult human, so in order to completely blow up something with greater mass, the technique must be applied multiple times on the object with the markings spaced apart from each other so that they do not cancel each other out. Which is something only an experienced user is capable of.
Limitations naturally exist however. The technique cannot be used on living things or the wood created by Mokuton users, as the mark will simply not form. Things infused with chakra aren't affected by the spell either, for the powers presence simulates life well enough to cause the spell to fail. Lastly, those resurrected by Edo Tensei fall into a border realm; while animate and "living" in a sense, their bodies do still consist of dead matter, thus the spell can be used on them.
Shadow Games (影遊び, Kage Asobi), a Senjutsu that enables the user to travel through one shadow to another nigh instantaneously, as long as neither of them is infused with chakra. Using their own shadow as a gateway, the user enters the void between dimensions and exits out of another shadow. Although all shadows present themselves as holes in the void through which the user can see the outside world, it is easy to lose one's bearing while in there. This makes attempting to find an exit that isn't in one's immediate line of sight before entering extremely risky, as the user can easily get lost and end up somewhere unknown if not lethal.
When the user enters or exits out a shadow, it will cause a water-like ripple effect on the surface of the shadow. As the spell only allows those with the same Demonic Chakra signature as the user to enter the shadow, it is impossible for an enemy or ally to take advantage of it. Ninjutsu that manipulates shadow cannot be used on shadows that are under the influences of this technique.
Flying Fox (飛狐, Hiko), a Senjutsu that grants the user the ability to float weightlessly in the air, and move about freely by surrounding the user's body with Demonic Chakra. The user is unaffected by gravitational ninjutsu or strong winds while using this technique. The technique however, cannot support more than twice the user's weight. If the user tries to carry something as heavy as themselves, they will find themselves losing too much Demonic Chakra too quickly to maintain the technique.
Shape Shifting (変化, Henge), a Senjutsu that is not unlike the Transformation Technique that Shinobi uses. The user can shape shift into another person, animal, plants, and even inanimate objects. The transformation will be exactly like the genuine article, so it will be impossible to tell the two apart even with the aid of doujutsu and chakra sensing abilities. One way of identifying the fake is by spotting the fox tail that often appears when the user is under a lot of stress, or if an inanimate object happens to move on its own. The transformation is permanent until the user undo the technique. If whatever the user transformed into is killed or destroyed, the technique will be undone automatically, reverting the user back to their original form completely unharmed.
Phantasm Boundary (幻境, Genkyō), a high level Senjutsu that drags anyone the user desires into a carbon copy of the real world by consuming a tremendous amount of Demonic Chakra. Time flows differently within this space, a day here would only be a second in the real world. The only ones in this world are those who were dragged into it and the user. Any destruction done to the surrounding will not be reflected upon the real world. If the user were to be defeated or leave this world, it would collapse, sending those trapped inside it back into the real world unharmed.
Senbi no Yōko is the only known user of this technique. The technique was created in order for it to face someone from the human world without bringing disaster to all of humanity.
Fox Possession (狐憑き, Kitsunetsuki), a Senjutsu that enables a Yōko to possess a human body temporarily, giving the possessed human access to the Yōko's Demonic Energy in exchange for their life force. For that reason, this technique is forbidden, and can only be used on humans that have signed a summoning contract with the Yōko. The possessed human will usually temporarily gain fox-like features such as fox ears, enlarged canines, sharp nails, and one or more tails. This technique can only be performed by Demon Foxes.