Byakuya Kuchiki (朽木 白哉, Kuchiki Byakuya) is the Captain of the Sixth Division in the Gotei 13. His lieutenant is Renji Abarai. He descends from one of the four great noble families of Soul Society, and as such he is the embodiment of pride and discipline, intending to be a role model for all Shinigami.
Due to an oath he took, he strongly supports the punishment of his adopted sister, Rukia Kuchiki, after she is abducted and sentenced to death for giving her powers to Ichigo Kurosaki, thus he becomes the fiercest opponent of the latter, when he comes to Rukia's rescue. After being defeated by Ichigo and learning the truth behind Rukia's planned execution, he becomes slightly more lenient and even more protective towards his sister and her Ryoka friends. Later, just like the other Captains, he is involved in the war between the Arrancar and Shinigami. He ranked 7th in the most recent popularity poll with 4,010 votes, edging out Orihime Inoue by 35 votes. Senbonzakura, Byakuya's zanpakutō, was voted the 5th most popular zanpakutō in a recent Bleach Poll.
Little is known about Byakuya's early history, except that 110 years ago before the current time he was a young boy, rash and hotheaded and somewhat similar to Ichigo in personality. He would spend countless hours training, in perpetration of taking over the leadership of the Kuchiki family and the 6th Division from his grandfather, Ginrei Kuchiki.
He used to be teased, usually it seems to his annoyance, but still regularly played tag with the older Yoruichi Shihōin using Flash Steps, though he never was able to beat her, a score that upholds to the current time.
Around 55 years before the current time, Byakuya married Hisana, who was then a commoner from Rukongai; therefore he broke the rules by accepting her into the noble Kuchiki family. Shortly before her death, Hisana asked Byakuya to find and adopt her biological sister, Rukia, whom she had abandoned as a baby. She also made him promise that he would not tell Rukia about her real family, for she believed that by abandoning Rukia when she was younger she was not worthy to be called her sister.
Byakuya about to adopt Rukia Kuchiki into the Kuchiki clan.
One year later, Rukia entered the Shinigami Academy; shortly after, Byakuya found her and immediately adopted her into the Kuchiki clan. By adopting her Byakuya respected his late wife's final wish, but had broken the rules of his clan again. He later swore upon his parents' graves that he would never break the rules again, no matter what. As a result, he, though entirely apathetic on the surface, is actually deeply conflicted with the matter of Rukia's execution: should he intervene, it would require breaking the promise to his parents and the rules again, but should he do nothing, he would fail to fulfill the last promise he made to his dying wife to protect Rukia as his own sister.
It is implied that Byakuya Kuchiki became Captain of the 6th division less than 50 years before the main Bleach storyline (shortly before Rukia had entered the Gotei 13). Gin Ichimaru became Captain of the 3rd Division at the same time, and Gin would commonly start pointless conversations with Byakuya during times they crossed paths.