Killer B (キラービー, Kirābī; Viz "Killer Bee") is one of the major supporting characters in the series, a from and the of , the Eight-Tails.
At a young age, B along with several other children were gathered in order to select a tag partner for . Out of all the children gathered, B was the only person able to successfully perform the with A. As such he was given the name "B", and A stated they would be brothers from that day on. Since the age of five, B has been best friends with , whom he always greeted with a fist bump. After , the jinchūriki of lost control and killed along with seven other ninja on that day, B was chosen as its next . Soon afterwards, B suffered from similar prejudices against jinchūriki, not too different from that the villagers of and had against and respectively. However, he kept smiling and pushed himself to be the best jinchūriki that he could be, so that his brother wouldn't be hurt politically as the Fourth Raikage.
After his father's death, Motoi tried to kill B, believing it would also kill Gyūki and avenge his father, but B disarmed him easily, and despite the attempt on his life, bore him no ill will, which led Motoi to not speak to B for thirty years out of shame. B would later train with his brother on an , where there he would find the . There he learned how to control Gyūki in the blink of an eye. Some time after his training, B, alongside A, and other Kumo shinobi confronted and his small squad. When Minato moved to counter A's attack, B used a tentacle to push A out of the way, causing shock to the Konoha shinobi that he was Gyūki's jinchūriki. Some time since then, much like Naruto, B has become beloved in Kumo as the village's hero, or, as Motoi called him, the "Hero of Heroes".
When A became the Raikage, he forbade B from fully transforming into the Eight-Tails and restricted him from leaving the village, saying instead that he would become the guardian of the village and attack from within its walls.