Byakuya Kuchiki is the 28th head of the noble Kuchiki clan, one of the four great noble families in Soul Society. As such, Byakuya acts in an aristocratic manner — he seems always serene and apathetic towards other people, even when he is actually deeply conflicted. He is also extremely calm, even in battle, and is very seldom surprised by even the most drastic of actions. Ironically, when he was younger, he was quick to anger and very hotheaded, as noted by his grandfather, much like his lieutenant, Renji Abarai, and Ichigo Kurosaki. Due in part to his status in Soul Society, he generally acts indifferent, bordering on arrogance, to most situations that he is faced with as seen from how he rarely views his opponent worth his time. Despite this trait, Byakuya is a very perceptive man and is fully aware of the limits of his abilities and usually anything he states in comparison to an opponent is justified.
Byakuya strongly believes in law and order. As the head of one of the great noble families and as a Captain in the Gotei 13, he always works hard for a peaceful society. He feels that if someone in his position does not follow the rules as a good example, then no one will follow them. He believes that to maintain the order, all law-breakers must be punished, even if that goes against his own wishes. In spite of his icy and regal manner, Byakuya cares for and protects those important to him.
Byakuya is popular among the female Shinigami of Soul Society, and was voted number one in the "Captain we desire to release a photo book for" poll taken by the Shinigami Women's Association. He likes Japanese Cherry Blossoms, night time walks, spicy food, and bananas, but he does not like sweets. Similar to Sōsuke Aizen, he excels in calligraphy. He apparently is very fond of Calligraphy being the representative or possibly President of the Calligraphy Society.
As astonishing as it may seem, Byakuya seems to have a comedic side, as he not only attends the Lieutenant's meeting when Renji's absent, but also attends the meetings of the Shinigami Women's Association when Rukia's absent. As he puts it, "part of a Captain's responsibilities is to make sure the Lieutenant's responsibilities are taken care of," to which Renji asks why he goes to Rukia's meetings, which is only responded by a (rather perverted) smile similar to that of Gin Ichimaru's. He once jokingly remarks that he uses Senbonzakura to cut his hair. In one of the omake chapters, Byakuya claims that life in general is not supposed to be entertaining, and even makes up an idea for a game that is not really meant to be amusing.
Byakuya comically shares Rukia's poor artistic talent. During a sand-sculpture contest he creates the "Seaweed Ambassador," which despite its crude form, Rukia adores and believes Byakuya surpasses her in creativity. The Seaweed Ambassador has made several appearances in other omake chapters.
Having descended from noble stock, Byakuya is easily offended if his name is not used properly. As such, he seems to view Ichigo Kurosaki in disdain for always referring to him as such, though he never said anything to him to change that. Ichigo seems to be the only one to refer to Byakuya very informally (even his wife referred to him as "Byakuya-sama") so far with the exception of Yachiru, who refers to Byakuya by the nicknames "Bya-kun" or "Byakushi," but it is possible that Byakuya lets it slide, given that Yachiru is a child. He once calls Ichigo to his mansion in order to have a talk with the young Substitute Shinigami, but they were interrupted by Yachiru's appearance, who asked Ichigo to follow her elsewhere. After Ichigo's disappearance, it is revealed that Byakuya wanted Ichigo to refer to him properly, and to stop calling him by only his first name. When Byakuya talks with Ichigo, he calls him by his full name, Ichigo Kurosaki. In some golden cups, he sees his house had been altered by some tunnels, which are revealed to be Yachiru Kusajishi's handiwork. In one of the most recent, he discovered that Yachiru, Nemu Kurotsuchi, Rangiku Matsumoto, Nanao Ise, Isane and Kiyone Kotetsu, Soifon, and Yoruichi were having a tea party in his house, without his knowledge (his face is not shown when he sees the room's interior). Later, when he tries to border up the secret door, Yachiru reveals another to Byakuya's intense surprise, and his face is shown with dismay.