The physical attribute kitsune are most noted for is their tails — a fox may possess as many as nine of them. Generally, an older and more powerful fox will possess a greater number of tails, and some sources say that a fox will only grow additional tails after they have lived for a thousand years. After that period of time, the number increases based on age and wisdom (depending on the source). However, the foxes that appear in folk stories almost always possess one, five, or nine tails, not any other number.
When a kitsune gains its ninth tail, its fur becomes silver, white, or gold. These kyūbi no kitsune ("nine-tailed foxes") gain the power of infinite vision — they can see (and hear) anything happening anywhere in the world. Occasionally, they are also attributed "infinite wisdom," essentially omniscience. Similarly, in Korea, a fox that lives a thousand years is said to turn into a kumiho (literally "nine-tail fox"), but the Korean fox is always depicted as evil, unlike the Japanese fox, which can be either benevolent or malevolent. Chinese folklore also contains fox spirits with many similarities to kitsune, including the possibility of nine tails.
In some stories, kitsune have difficulty hiding their tail — usually the foxes in these stories have only one, which may be an indication that this is a weakness born of inexperience — when they take human form; the observant protagonist sees through the fox's disguise when the drunken or careless fox allows its tail to show.
Looking for the fox's tail is one common method of attempting to discern the true nature of the kitsune, but some sources speak of other methods to reveal its true shape. Sometimes, a shapeshifted kitsune will cast the shadow of a fox rather than of a human; other stories say that a transformed kitsune's reflection will be that of a fox. Foxes also have a great fear and hatred of dogs, even while in human form, and some become so rattled by the presence of a dog that they will revert to the shape of a fox and flee. Finally, a particularly devout individual may be able to see through the fox's disguise.

Powers of kitsune

Supernatural powers commonly attributed to the kitsune include, in addition to shapeshifting, possession (see kitsunetsuki below), the ability to generate fire or lightning from their tails or to breathe fire (known as kitsune-bi, literally "foxfire"), the power to manifest in dreams, the power to fly, and the ability to create illusions so elaborate as to be almost indistinguishable from reality.
They also have a special power to take the human into the spirit world with them, and if you accept coming with them, you can never return to the human world.
Some tales go further still, speaking of kitsune with the ability to bend time and space, to drive people mad, or to take such nonhuman and fantastic shapes as a tree of incredible height or a second moon in the sky. Occasionally kitsune are ascribed a characteristic reminiscent of vampires or succubi — these kitsune feed on the life or spirit of humans, generally through sexual contact.

"Star balls"

Sometimes kitsune are depicted guarding a round or pear-shaped ball, known as as a "hoshi no tama" ("star ball"). It is said those who obtain the ball can force the kitsune to help them; one theory says that the kitsune "reserves" some of its magic in this ball when it changes shape.

Kitsune as servants of the deity Inari

Kitsune are often associated with the deity of rice known as Inari. Originally kitsune were the messengers of Inari, but the line between the two has now become blurred to the point that Inari is sometimes depicted as a fox. There is speculation as to whether there is another shinto deity who is a fox him/herself, but little historical evidence to support this. Kitsune are connected to both the shinto and Buddhist religions.

Portrayal of Kitsune

In Japanese folklore, the kitsune are often presented as tricksters — sometimes very malevolent ones. The trickster kitsune employ their magical powers to play tricks on people; those portrayed in a favorable light tend to choose as targets overly-proud samurai, greedy merchants, and boastful commoners, while the more cruel kitsune tend to abuse poor tradesmen and farmers or Buddhist monks.
Despite their role as tricksters, however, a kitsune will keep a promise it has given and will strive to repay any favor it owes. Occasionally a kitsune will take a liking to and attach itself to a certain person or household; as long as it is treated with respect, it will use its powers for the benefit of its companion or hosts. As yōkai, however, kitsune do not share human morality, and a kitsune who has "adopted" a house in this manner might, for example, bring its host "gifts" of money or items that are in fact stolen from the host's neighbors. Any household suspected of harboring kitsune, therefore, tends to be treated with suspicion.
Kitsune are also commonly portrayed as lovers. These love stories usually involve a young human male and a kitsune who takes the form of a woman. Sometimes the kitsune is assigned the role of seductress, but often these stories are romantic in nature. Such a story usually involves the young man (unknowingly) marrying the fox, and emphasizes the devotion of the fox-wife. Many of these stories also possess a tragic element — they usually end with the discovery of the fox, who then must leave her husband. On some occasions, the husband wakes, as if from a dream, to find himself far from home, filthy, and disoriented, and must often return to confront his abandoned human family in shame.
Many stories tell of fox-wives bearing children. Such progeny of human-kitsune marriages are always human, but they are generally held to possess special physical and/or supernatural qualities, which are often passed to their children in turn. The specific nature of these qualities, however, varies widely from one source to another. Among those who are said to have inherited such extraordinary power is the famous onmyoji Abe no Seimei, who is said to be the son of a kitsune.

False etymologies of the word "kitsune"

The oldest known story of a fox-wife provides a folk etymology of the word kitsune. This story is an exception to the norm in that it does not end tragically.
In the story, a fox takes the shape of a woman and marries a human man. The couple spends many happy years together and have several children. The wife is ultimately revealed as a fox when, terrified by a dog, she reverts to her fox shape in the presence of many witnesses. She prepares to leave her home and return to the wild, but her husband says "Now that we have spent so many years together, and I have had several children by you, I cannot simply forget you. Please come and sleep with me." The fox agrees, and from then on returns to her husband each night in the shape of a woman, leaving again each morning in the shape of a fox. She comes to be called Kitsune because, in classical Japanese, "kitsu-ne" means "come and sleep," while "ki-tsune" means "always comes."
Some have suggested that the origins of the word "kitsune" may be an onomotopoeia. "Kitsu" was said to be the sound produced by foxes in Japan, much in the way that "woof" is said to be the noise dogs make in the West. "-ne" can be translated to mean "noise," and so the word "kitsune" can also literally refer to the sound produced by a fox. However, "kitsu" has not been used as representative of the sound foxes produce for some time; in modern Japanese the sound of a fox is said to be "kon kon" or "gon gon."

Kitsunetsuki

Kitsunetsuki (狐憑き or 狐付き; also written as kitsune-tsuki) literally means the state of being possessed by a fox. The fox was believed to enter the body of its victim, typically a young woman, beneath her fingernails or through her breasts. In some cases, the victim's facial expressions were said to change in such a way that they resembled foxes. Japanese tradition holds that the possession can cause illiterate victims to temporarily gain literacy.
He goes on to note that, once freed from the possession, the victim will never again be able to eat tofu, azukimeshi, or other foods favored by foxes.
Victims of kitsunetsuki were often treated cruelly in hopes of forcing the fox to leave. It was not unusual for them to be beaten or badly burned. On some occasions, entire families were ostracized by their communities after a member of the family was believed to be possessed.
In Japan, kitsunetsuki was a common diagnosis for insanity as recently as the early 20th century. Possession was the explanation for the abnormal behavior displayed by the afflicted individuals.
Kitsunetsuki is also an ethnic psychosis unique to Japanese culture, which causes its victims to believe they are being possessed by a fox. Some of the symptoms of kitsunetsuki are cravings for rice or sweet red beans, listlessness, restlessness, and an aversion to eye contact. It is similar to, but distinct from, clinical lycanthropy