Killer B

is a ninja from Kumogakure and the Jinchūriki of the Eight-Tailed Beast. He is a black, musclebound Cloud shinobi, who appears to dislike light. On his right shoulder, he has a tattoo that says "iron"; and on his left cheek, he has a tattoo of a bull's horn. He also carries seven swords.

Personality
It seems that he demands respect from those under him and asks to be called "Mr. Jinchūriki" or "Mr. Eight-Tails". He also appears willing to speak in song more specifically in rap style, even when confronted with potential threats. He will even stop in a middle of a fight to write whatever rhymes come to him.

Hunt for the Eight-Tails
Team Hawk, after discovering that the Eight-Tails was training in the Unraikyo Mountains traveled up the mountain. He revealed himself after appearing to contain his Tailed Beast. When Suigetsu attacked him, he easily overpowered him, and uses Suigetsu's sword to defeat Jugo afterwards. He later shows an unorthadox sword style where he manages to hold all seven of his swords in a rather awkward pose, this is deceiving as his seven sword style is extremely formidable and he even fatally wounds Sasuke Uchiha.

As he moves in to finish Sasuke, Suigetsu comes to save him while Jugo attacks from behind. Even with the three fighting him at once Kira appears unfazed by their attacks. When the three do a triple damaging attack to him, he somehow moves extremely quickly to a same position relatively far away. Finally getting annoyed with Team Hawk, Kira decides to go home and have some whiskey, but Karin senses his location. As Sasuke is rocketed to his position, Kira announces he will unveil the "Eight One". Kira Hachi developed his own demon chakra shield, similar to Naruto's chakra shield, and proceeded to attack Hawk, and in the end blasted a hole in Sasuke's chest and neck before completely releasing the full power of the Eight-Tailed beast.

Abilities
The Eight-Tails Jinchūriki appears to be able to fully transform into his Tailed Beast with great ease, similar to his fellow Cloud shinobi, Yugito Nii and is clearly confident of his own fighting style.

His physical strength and taijutsu skill is immense. He is easily capable of disarming a skilled opponent with his bare hands, and proficiently wielded Suigetsu's giant sword seconds after picking it up. His specialty, however, is wielding his seven swords, which he does in an odd way, holding them in between the joints of his arms and left leg, his stomach and the left side of his neck. As awkward as it appears, he is quite skilled with this, spinning around like a buzzsaw and overwhelming his opponent with all of the varying swings. He is also capable of seamlessly releasing some of the swords to fight in a more conventional style, giving him great versatility. When he does find an opening, he can impale his opponent with most of his swords at once. While fighting with this style, he was effortlessly able to defeat Sasuke, and would have killed him if not for Karin's healing abilities. He has a very strong defense, as seen when Sasuke nailed him with a full blown Chidori, and also when Jugo slammed him in the face with a curse seal powered arm, only to have him say "Those weaklings are really annoying"

During the battle with Sasuke he displayed the ability to conduct chakra down his blades to increase their cutting power like Chidori Current does with Sasuke's Kusanagi Sword.

Kira Hachi also has the power to create his own chakra shield when drawing on his demon's power. It is because he has control over his own demon he is able to break Tsukuyomi because he used the Eight-Tailed Beast to disturb his chakra. He is also able to create his own chakra shield without much effort and become the Eight-Tailed Beast itself.

Trivia

 * His Sword style is reminiscent of Roronoa Zoro's Santōryū in One Piece (a fellow Shonen Jump manga) in that he uses an odd number of swords as well as holding a sword in his mouth.
 * He quoted Muhammad Ali's famous line, "float like a butterfly, sting like a bee" in chapter 411.
 * Though not his confirmed name, Kira Hachi is the fan name given to this Jinchūriki (the other being "Mr. Eight-Tails"). Also, it is hinted he hails from the Yotsuki clan.