In the anime, it is revealed that when Kurama, the Nine-Tails, attacked Konohagakure, it left a lot of residual chakra in the surrounding areas. The chakra was later gathered by Kazuma, one of the Twelve Guardian Ninja, who wanted to create a jinchūriki weapon for the Land of Fire to use against Konoha. After five years of experimentation, he finally was able to implant Kurama's chakra into the cells of his son, Sora. Because Sora does not have the tailed beast sealed within him, but only has his cells combined with its chakra, he is referred to as a pseudo-jinchūriki.
Even though Sora does not have the actual tailed beast inside of him, the chakra implanted within him can react to Kurama within Naruto Uzumaki, as it somehow called out to him when Naruto was about to be killed by Fūka. Unlike Naruto, he doesn't have as much chakra as Kurama would usually generate when Naruto is in his demon fox shroud, nor can he control it. Instead, Sora becomes greatly influenced by the fragments of Kurama's psyche within its chakra, threatening to kill anyone who stands in his way.
Initial Jinchūriki Form
Unlike Naruto, who has a stable and controlled combination of his own chakra and Kurama's chakra (because of the Fourth Hokage's seal), Sora can't control the chakra added to his cells. To stabilise this, his father applied a sealing jutsu on Sora several times to keep him and the chakra under control. In contrast to Naruto, in which the chakra forms like flames around him, it forms a solid chakra shroud around Sora with no tails.
When Sora feels frustrated or is in a state of great anger, the chakra can change his right arm into a demonic form. It would seem that he is not aware of the change of his arm, and only first noticed it when his father told him. In this form, Kurama's chakra does not fully control Sora's body.
When his father would stop applying the seals or when he completely releases it, he uses the Five Elements Unseal, which the chakra can run loose and slowly take over Sora's body.
Like Naruto, when the chakra is released from Sora in large amounts, a demon fox shroud will form around Sora. Initially and slowly, he will begin to grow a chakra tail. Like with Naruto, during this transformation, Sora's hair becomes spiked, his canines longer and sharper, and his eyes turned to slitted fox-like eyes. Unlike Naruto, he has spiked projections growing from his cheeks. In this form, the chakra surrounding him damages the people around him and inflicts a painful burn to anyone that comes into contact with it for too long.
Sora cannot maintain control of his body or emotions for very long, eventually giving into Kurama's urges and gaining a will to kill and destroy everything. Naruto never displayed this problem until his fourth tail emerged.
Due to Sora's increasing levels of anger, he skipped the two-tailed form and grew the third chakra tail. Like Naruto, he begins crouching on all fours. However, unlike Naruto, he has now given in to Kurama's chakra completely, and will only growl and roar, something Naruto never really displayed during his three-tailed form, where he seems to still be in slight control.
Like Naruto, Sora will also gain the ability to blow his opponent away using a simple roar of chakra in this form, and has also displayed the ability to use the extended chakra arm.
Releasing even more chakra than before, even from his mouth, and growing a fourth chakra tail, Sora's skin begins to slowly peel off and in an instant explosion of chakra he is completely covered in the demon fox shroud, resembling a miniature Nine-Tails. With Sora, the demon fox shroud takes on a yellow, orange colour, while Naruto's shroud is more red.
Also, Sora's legs are thinner and longer, and the spikes sprouting from his face in his earlier forms are visible in the shroud, alongside his spiked hair, being slightly bigger than when Naruto transformed. In this form, he has absolutely no control of himself.
He possesses the same powers like Naruto in his four-tailed form, but his attacks, like the Tailed Beast Ball, seems to be significantly weaker than Naruto's (Sora's attack could only destroy a small part of a forest). Yamato speculates that this is because Sora's body is too frail to keep up with the incredible chakra the four-tailed form gives him.
- It was shown that Kurama's chakra sealed within Sora needs a human vessel to maintain its form. Since it could not find another vessel when it escaped Sora, Kurama took back his chakra