In my head

Lore
Kitsune (狐, きつね, Kitsune) is the Japanese word for fox. In Yōkai folklore, kitsunes are viewed as shapeshifters that can have up to nine tails. Stories depict kitsune foxes as beings of intelligence and magical abilities that only increase in power with age and wisdom. Some have been depicted as tricksters, but often they are also portrayed as faithful guardians, friends, lovers, and wives. Despite being deemed as fox spirits, kitsune are not ghosts. The word spirit is used to reflect a state of knowledge or enlightenment, a state any long-lived fox can reach.

Kitsunes at their core, are simply foxes. The length of one's lifetime is what differentiates them from the fox species. Only kitsunes who have lived for 100 years have the ability to shape shift into a human form, and it is only then that they gain their ninth tail. Prior to living 100 years, they live their life as any fox would. While kitsunes do have their own human form, they also have the ability to mimic the exact appearance of another human. Often times this is why kitsunes have been viewed as spirits of trickery.

There are two common classifications of kitsune. The zenko (善狐, good foxes) are benevolent, celestial foxes associated with Inari; they are sometimes simply called Inari foxes. On the other hand, the yako (野狐, field foxes, also called nogitsune) tend to be mischievous or even malicious. Local traditions add further types. For example, a ninko is an invisible fox spirit that human beings can only perceive when it possesses them.

Physically, kitsune are noted for having as many as nine tails. Generally, a greater number of tails indicates an older and more powerful fox; in fact, some folktales say that a fox will only grow additional tails after it has lived 100 years. One, five, seven, and nine tails are the most common numbers in folk stories. When a kitsune gains its ninth tail, its fur becomes white or gold. These kyūbi no kitsune (九尾の狐, nine-tailed foxes) gain the abilities to see and hear anything happening anywhere in the world. Other tales credit them with infinite wisdom (omniscience). A kitsune may take on human form, an ability learned when it reaches a certain age—usually 100 years. As a common prerequisite for the transformation, the fox must place reeds, a broad leaf, or a skull over its head.

Foxes and humans have lived alongside each other since ancient Japan, which is when legends were born about the creatures. Through the many years, kitsune were heavily linked with the Shinto deity Inari. Serving as messengers for the deity which only reinforced the belief that kitsunes held a sort of supernatural significance. When it comes to the wizarding world, the kitsune species has been dated as far back as the magical Imperial family of Japan. The deceased half-brother of the then Emperor Suizei, Taigishimimi, had a child with a witch concubine. As the story was told through Japan, different iterations of the story had been told, one of which described the witch concubine as a kitsune or fox spirit. If this version of the story is believed to be true, the magical Imperial family of Japan would in fact have direct kitsune lineage in their blood.

Throughout history, kitsune have maneuvered their way through the world. Balancing a fine line between living in the magical realm and tricking muggles in their realm. Often times in Japanese culture, if a muggle wasn't privy to the concept of wizards and witches, a sighting of one using magic was often explained as a kitsune as it was more widely known to them.

Sources:
 * https://yokai.fandom.com/wiki/Kitsune
 * http://www.mythicalcreaturesguide.com/page/Kitsune

Abilities

 * Kitsune are able to project and retract canine-like claws from their hands.
 * Kitsune have the ability to manipulate fox-fire as they please, usually manifesting it in the form of fire, electricity, or light. In a fox form it is most commonly expelled from their mouth or tails, while in a human form it can be manipulated by their hands.
 * A more enlightened kitsune may even be able to manipulate fox-fire to the point of using it as a form of mobility by becoming fox-fire. It can also, while more more taxing on the kitsune, be used for hypnosis or draining of one's life/energy.
 * Kitsune are able to manipulate and create illusions in order to trick or distract a target. These illusions can consist of things the target is seeing, hearing, feeling, smelling or tasting. While younger kitsune and most half-kitsune can only create an illusion around them and for a short period of time, a more enlightened and older kitsune could create an entirely detailed world.
 * Kitsune are able to induce insanity upon a target. This could be used to alter one's perception of an enemy/ally, cause delusion, or turn someone so paranoid they lose all control over themselves.
 * Full Kitsune have been known to be able to possess a person or an object for a short period of time.
 * All kitsune are able to shapeshift in some form.
 * A full kitsune that has lived for 100 years will gain the ability to have a human form. Being able to choose between any gender, or appearance they would please. Though a kitsune is more likely to have just one human form, there is nothing stopping them from shifting into a different human appearance.
 * Half or part-kitsune on the other hand are only able to shift into a fox, with some more minor appearance alterations. These would include hair length or colour, eye colour, and maybe some more minor physical aspects of a human body.
 * While in a fox form a kitsune would obviously have a tail, it is also possible for their tail to manifest in their human form. If a kitsune has all nine tails, all nine can even be manifested into their human form. These tails can be used for things such as fox-fire manipulation, added limbs, protection, or combat.
 * As kitsune are a vulpes canine, with that naturally comes all vulpes traits and abilities. This would include; enhanced speed, endurance, senses, vision at night, stamina, strength, and stealth. With this also comes a new sense of a powerful bite force and fur generation, as well a more predator like instinct.
 * They have the ability to manipulate and control one's dreams. Bending a target's dreams to their own will while also being able to have full control and awareness during their own.
 * A kitsune is able to manipulate or enhance one's feelings of love or lust, whether towards themselves or another person. Using this often to get others to do their own bidding or play tricks on others by making them fall for someone.
 * Those of higher enlightenment may even be able to manipulate and utilize the elements around them. It is because of this that some stories detail there being thirteen types of kitsune.
 * Tengoku (Heaven, Celestial, Light, Prime)
 * Kukan (Void, Dark, Nogitsune)
 * Kaze (Wind)
 * Seishin (Spirit)
 * Kasai (Fire)
 * Chikyu (Earth)
 * Kawa (River)
 * Umi (Ocean, Sea)
 * Yama (Mountain)
 * Mori (Forest, Woods)
 * Sanda (Thunder)
 * Jikan (Time)
 * Ongaku (Music, Sound)
 * While this is primarily dispelled, many do still believe that there are thirteen types of kitsune species despite the universally accepted two types of zenko and yako.

Weaknesses

 * When a full-kitsune takes on a human form, they may keep some trait that will reveal their true form. A tail, shadow/reflection, vertical pupils, and facial features being the most common.
 * Furthermore, carelessness and/or drunkenness may reveal the true form of a full-kitsune.
 * Dogs can detect when a kitsune is near or if someone is a kitsune.
 * Until they gain their ninth tail, kitsune are essentially physical foxes. This however does not apply to half-kitsune.
 * It is possible for a kitsune to become consumed by negative emotions. This can happen quite easily and even lead to death.
 * Those of faith may be able to see through a kitsune's illusions, and may even be able to force them into their true form.
 * Kitsune are vulnerable to the opposite alignment of themselves. For example zenko are vulnerable to yako, and vice versa.
 * Furthermore, it is highly possible a benevolently aligned kitsune is also susceptible to dark magic as a whole, with similar effects on malevolently aligned kitsune and magic or rituals that counter darkness.

Misc

 * As a kitsune gets older, their natural abilities become stronger with age. Steadily growing in strength as they age, this is depicted by the amount of tails a kitsune has.
 * As a species, kitsune have decelerated aging and a sense of semi-immortality. While their mind and powers strengthen with age, their physical human body would stay unchanged for the most part past their prime adulthood form.
 * The average lifespan of a full kitsune is 1000 years old, before they are able to "ascend" the mortal realm.
 * It is assumed half or part kitsune can live for just as long, but it is more than likely halved.
 * Kitsunes possess a continuously increasing and expanding intellect, with no known limits. This can lead them to become practically omniscient.
 * Kitsune grow more powerful when the moon is present. With their abilities becoming more empowered by the moonlight and their strength increasing.

Traits

 * It is common for kitsune have a fear or a hatred of dogs. While it may not be as common for half-kitsune, it is still prominent in the species.
 * While in a human form, their features are often canine like with sharp facial features and teeth. Thus, children of a kitsune would possess these qualities as well.
 * Kitsune have an aura that surrounds them. While the normal eye may not be able to pick up on it, those with an enhanced sense of being or knowledge would be able to see it and thus detect the alignment of a kitsune because of it, finding out if they are good or bad.