Fukai's Jinchūriki Forms

Being Gyūki's jinchūriki before Killer B, Fukai could access its power, though he was unable to obtain full control over the beast itself. After being reincarnated by Kabuto Yakushi during the Fourth Shinobi World War, Fukai was shown to be able to use a tailed beast cloak.

Version 1
Before accessing Version 2, Fukai could manifest a tailed beast cloak.

Version 2
After being reincarnated, Fukai could easily manifest a "Version 2"-like chakra cloak with eight tails, very similar to Killer B's Version 2, though there are some differences in the appearance: the blue mark on Fukai's right cheek still appears in this form, and the left horn has a green aura, probably due to the fact that it was the part of Gyūki's body that was recreated by Orochimaru. Also, unlike B's Version 2, the horns point forward rather than pointing upwards. In this form, Fukai had the same abilities as Killer B, being able to create a skull of the Eight-Tails for the Lariat, as well as firing a weaker version of the Tailed Beast Ball, which he could also fire in rapid succession.

Partial Transformation
Though he never gained full control over Gyūki, Fukai could manifest a small part of its tails, but it is unknown whether it was the beast trying to free itself or not.