If he is not contained, or if the Kyuubi is not resealed and Naruto grows all nine tails of the Kyuubi, he will, in a sense, die, and the Kyuubi will once again be released to wreak havoc on the world. At that point, he completely loses control of himself and he will begin to attack everyone - friend or foe. So far, in both the manga and in Naruto Shippuden, we have only seen up to four of Naruto's tails. The number of tails that grows out of Naruto, the stronger he becomes and the more he loses control of himself. In the anime, when Naruto succumbs to the Kyuubi's temptation of power, his charka leaks out and forms like 'tails'.
The number of tails the kitsune has indicates its age, its wisdom, and its strength. The kitsune can have several tails, ranging from one to nine. However, it most commonly transforms into a beautiful woman, a seductress, much like 'Naruko', Naruto's female form when he does his Oiroke no Jutsu. The kitsune can transform into a human being, a skill it learns when it reaches a certain age, usually 100. In fact, the Kitsune is often called a 'trickster' and incidentally, this is how Naruto is portrayed at the beginning of the story.
The fox, as portrayed in Japanese folklore, is a cunning creature, intelligent but mischievous. Translated, Kitsune means 'fox'. Indeed, the Kyuubi is based on the Japanese mythological creature called the Kitsune. Kishimoto-sensei certainly didn't just pull this Kyuubi legend out of his hat. Kyuubi's Origins But where does the Kyuubi's origin lie?
This rendition of the Japanese mythical creature, the Kitsune, is one of the most mysterious and interesting characters in the anime. Few things in the anime, Naruto, can charge the atmosphere with as much as excitement and as much awe as when Kyuubi appears on screen.