Byakuya is an arrogant and serious young adult who originally saw himself to be more superior than the others due to being the heir to an extremely successful family business. He is extremely reluctant to admit to any mistakes he might have committed, and constantly refers to the other students as "amoebas" and "plebeians". He has a deviously manipulative tendency, as he often expressed irritation from Toko Fukawa and Genocide Jack's obsessive behavior towards him, but often used it to his benefit by ordering them around. He has also betrayed their trust more than once for his own personal gain.

He is often cold, blunt, and reserved, preferring to work alone and mocking the others' attempts to be cooperative, even bluntly stating that they are not friends. However, he does not appear to be as actively mean as he seems. Usually when he answers to the other students with cruel words, it is because they bothered him when he wanted to be left alone. It also appears that he was taught strict manners by his family, as he refuses to use swear words and is completely disgusted by vulgar words and behavior, and anything he considers barbaric. Notably, his overly serious personality often makes him quite comical, especially if he is with Toko or Genocide Jack. For example, he has used the word "effing" in order to avoid swearing, and once ran away to escape Toko in a comical manner. Moreover, due to his upbringing, he has poor knowledge on certain things that are considered common knowledge. He is confused by the idea of people making their own food, as his food is always prepared by a chef, and he doesn't know what toy vending machines are.

Competition, challenge and victory are a key part of Byakuya's life, and he even stopped making millions in a day simply because it was too easy and just killing time. He is shown to be very confident in his abilities and does not seem to consider failure even an option. In his Free Time Events, it's revealed that he had to work really hard and earn his current status, and thus he is very angered and offended whenever people assume that he got his title simply by being fortunate enough to be born into a rich family. He also appears to have genuine respect for the half-siblings he had to beat in order to reach his status, and is motivated to persist out of respect for those he defeated. However, because he was raised in highly competitive environment, he thinks people only think about themselves and he dismisses emotional ties as petty and unimportant.