The origin of the kitsune legend is still unknown but is most likely related to this japanese folktale. Ono, who lived in Mino, often spent his time longing for female beauty (a wife). He met her one night on a moor and decided to marry her. Although with the birth of their son, Ono's dog also gave birth. The pup's opinion toward Ono's wife harshened as it grew and one day she begged her husband to kill it (of course he refused). At last one day, the dog had enough and attacked the woman. She then lost all her courage, turned back into a fox, and left. Then Ono cried out to her, "Even though you are a fox, you are the mother of my son and I love you! Come back when you please; you are always welcome."
Every night, she snuck back to Ono's house and slept in his arms.
The reason why that story is the most believable one is because kitsune also means sleep if pronounced kitsu-ne, and always comes if pronounced ki-tsune.
In many other folktales, Kitsune are known to be tricky by taking over women's bodies in a state called Kitsunetsuki. During Kitsunetsuki, the woman's face takes on a more fox-like appearance. Also, the possessed woman recieves a ball of skin that if poked, instantly moves to another place on the body. The kitsune will often embarass the vessel in various ways. Some may even relate kitsune to the succubus legends.
Although mainly reffered to as vicious pranksters, others consider them yokai which is a japanese spiritual being. They are gifted with many powers including long life, which is measured by how many tails they have (9 in all). However, even though they are known as spirits, they should not be confused with ghosts. The reason why they are considered spiritual, is because they are said to be related to Inari, god of fertility. They are also symbols of wealth. It is often honorable, to dress a kitsune statue with an apron with red and white polka dots.
They are often described as having a ball with them, which if seperated, the kitsune will die.
Another legend is a woman who was called the jewel maiden fled from China to Japan where she became part of the emperor's harem. When the emperor started to become ill and called to her, one of his advisors shoved a mirror in her face and the reflection was that of a nine tailed fox. She was draining his life force by staying close to him. She fled to an island and sulked there until she turned into a stone that not even the clouds could approach without being destroyed.