Sora's Jinchūriki Forms

When the Nine-Tailed Demon Fox attacked Konohagakure, it left of a lot of chakra in the air, and that was later gathered by Kazuma, one of the 12 Guard Ninjas of Fire, who wanted to create a Jinchūriki weapon for Konoha. After five years of experimentation, he finally was able to implant the demon fox's chakra into the cells of his son, Sora. Because Sora does not have the Tailed Beast sealed within him, but he only has his cells combined with its chakra, and he is refered as a Pseudo Jinchūriki.

Jinchūriki Form
Unlike Naruto, who has a stable and controlled combination of his own chakra and the Nine-Tailed Demon Fox's chakra, Sora can't control it's chakra added to his cells when his frustration or great anger which can change his right arm into the form of a demon. It would seem that he is not aware at all about the change of his arm to a demonic form and has first noticed it when his father told him.

Because the Nine-Tailed Demon Fox is a chakra monster, it's small amount of chakra implated within Sora can react to the chakra of the real Nine-Tailed Demon Fox inside Naruto as it somehow called out to him when Naruto was about to be killed by Fuka