Byakuya is a cold and self-centered person who is very reserved. He is not interested in co-operating with others due to his own sense of self-superiority, and his opinion that others are, on the whole, lesser than him. This sense of superiority and black-and-white worldview comes as a result of his upbringing. Because Byakuya was raised in such a highly competitive environment of "haves" and "have-nots", he thinks all people only think about themselves and he dismisses emotional ties as petty and unimportant. Due to his lack of emotional ties with the other students, Byakuya was able to emotionally distance himself from the horrors of the Killing School Life, and thus proved to be one of the most competent and insightful investigators in the group due to his high level of intelligence. His compulsive competitiveness caused him to treat the Killing School Life as simply a game, and one he fully intended to win. However, Byakuya's emotional detachment and lack of empathy towards the others sometimes made it very difficult for him to understand the reasoning for why people would behave altruistically or based on pure emotion.

 He eventually became not just a serious character but often a butt-monkey, as he can sometimes appear comical due to how serious and dramatic he can be with his words and belief in his own superiority and how it frustrates the other students. Due to his unusual upbringing, it's been shown that he has a bit poor knowledge on certain things that are considered common knowledge. Despite still maintaining his cold and dismissive demeanor towards others, the Killing School Life did appear to alter his worldview and make him more respectful and co-operative with others, though still denies that they are his friends.

If you could sound similar to his English VA, Jessie James Grelle, that would be great, but it is not required!

I don't have any English VA examples as there is not many I can find on Youtube, so if you could try and match the dub voice, it would be great, but again, it is not necessary.