Naruto Uzumaki's Jinchūriki Forms

When Naruto Uzumaki, taps into the Nine-Tailed Demon Fox's chakra, it increases every physical aspect of his body. Increased healing, great amounts of chakra, a powerful shield, and the ability to become poisonous when mixed with blood. Naruto has unique access to the demon fox's chakra due to the seal the Fourth Hokage placed on him, which sealed the fox's Yin chakra, giving Naruto control over the Yang chakra, allowing him to combine it with his own and make it easier to use.

Jinchūriki Form
By simply tapping into the demon fox's chakra, Naruto's blue eyes turn red, his nails and incisors grow long and sharp, and his whisker marks become more feral. Depending on how much chakra is unleashed, red chakra could glow around his body in an untamed way. Naruto first reached this form, when Sasuke Uchiha was apparently killed by Haku causing pure rage to take over allowing the demon fox's chakra to leak out of the seal.

Even though this is the weakest state of his Jinchūriki forms, it is still a deadly foe as it increases his physical strength well above most shinobi. Until special training from Jiraiya, Naruto could only reach this state through rage or if his life was in imminent danger but after having a inner talk with the demon fox, he is able to tap into the demon fox's chakra on his own, or by simply telling the fox to give him some power.

One-Tailed Transformation
During Naruto's battle with Sasuke at the Valley of the End, when Naruto was at the mercy of Sasuke, the demon fox told Naruto he should be grateful to him and gave him more chakra. The amount of chakra was so great that it it leaks out of his body in a denser state. All the phyiscal traits of the basic Jinchūriki form are present with one major bonus; the red chakra becomes a complete shield around his body, in the shape of a fox, complete with long ears and a tail. In his one-tailed transformation, Naruto fights more like a beast. Instead of using his fists, he instead uses his sharpened claws. While he can stand on his own two feet, he can move at greater speeds on all fours. But his most powerful weapon is the chakra itself. The bubbling chakra appears to have a mind of its own as a strike that was meant for Sasuke missed, the chakra itself stretched off Naruto's arm and hit Sasuke before he could react. As the chakra as a mind of its own, it makes it extremely difficult, if impossible to predict Naruto's movements, as Sasuke was able to see Naruto somewhat perfectly, but couldn't predict what the chakra would do with the Sharingan. The chakra can stretch far from the body, as Naruto was shown using his "arms" to attack Sasuke from great distances, at one point being on an opposite side of the valley, and still attacking him with the chakra arms. The shield around his body appears to be impenetrable, comparable to Gaara's Ultimate Absolute Defense: Shield of Shukaku.

Two-Tailed Transformation
After catching the Akatsuki member, Deidara, and beating what he thought was Deidara to pieces only to realize he had been attacking a substitution, his anger at losing Deidara and not being able to avenge Gaara's death caused him to slip into his two-tailed transformtion. His physical characteristics match the first two forms, but his red eyes and incisors grow larger, his lips get a black outline, similar to fox gums. The chakra shield's only difference between the one-tailed transformation and the two-tailed is the extra chakra tail that has grown. While in this state, Naruto is still in control of his body, though to what extent is unknown. In the anime, he attempted to attack Kakashi Hatake, when the latter tried to calm him down, and possibly in his mind, tried to stop him from finding Deidara. The amount of chakra being produced by the two-tailed transformation is so great, that even Naruto's shadow clones, doubled over in pain from the chakra.

Three-Tailed Transformation
After Orochimaru revealed himself to Team Yamato, and after baiting Naruto with news of Sasuke, Naruto went on a rage and first attacked him in his one-tailed state. When that failed and due to further baiting from Orochimaru, Naruto skipped the two-tailed transformation all together, and went straight into his three-tail transformation. The three-tailed looks exactly like the two-tailed, again the only difference being the number of tails. The amount of chakra produced from this form is devastating. The very air around Naruto begins to hurt. This is the strongest form Naruto can reach and control. This form gives Naruto the new ability to yell supersonic waves that can cause great destruction.

Four-Tailed Transformation
When Orochimaru faced the three-tailed transformation, in desperation and anger, he turned to the demon fox, and slipped into the fox's grasp. The demon fox's chakra begins to burn its way through Naruto's body, destroying his skin, and rapidly healing it at the same time, eventually covering his entire body in a mix between the fox's chakra and his own blood, making the shield poisonous. Everything from his face to his chakra tails becomes completely solid, his eyes losing its characteristics and becomes empty glowing circles surrounded by chakra. In this state, in effect Naruto takes the place of the demon fox inside the cage. The demon fox has complete control over his body, making the boy's body a mere skeleton for the fox's chakra, and making every living thing in its way a target. The four-tailed transformation has all the benefits of the other tails, such as firing red chakra blasts and possessing great strength, with upgrades. The energy of the chakra is enough to destroy two of the three Rashomon gates of Orochimaru.

In the end, despite being its strongest Jinchūriki form the four-tailed transformation is Naruto's greatest downfall. Because the demon fox's chakra is constantly destroying and creating new cells, it can shorten his life-span if used too long, similar to Tsunade's Creation Rebirth. Naruto first slipped into this state when he was training with Jiraiya, because the latter used the toadkey to "twist" the seal the Fourth placed on Naruto. A small "twist" of the seal unleashed the four-tailed transformation and almost killed Jiraiya.

Jinchūriki Chakra Control
In the event of the demon fox manifesting, Naruto's sensei, Jiraiya, prescribes a special written seal that is to be placed on Naruto's body. This seal suppresses the demon fox's chakra and restores Naruto to his normal self. In addition, Yamato has demonstrated a technique that will reverse Naruto's demon fox transformation, enhanced greatly by the First Hokage's necklace that Naruto wears.

Sasuke also demonstrates the ability to forcefully suppress the demon fox's chakra, an ability of the Sharingan that allows a user with it and the kekkei genkai to enter peoples subconcious and suppress uncontrollable chakra. To parallel the fox's apparent connection with the Uchihas, Itachi Uchiha of Akatsuki is originally assigned to capture it as part of the organization's goal of obtaining all the tailed beasts, but this task is later given to Pein.