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; Byakuya had to prove his worth in battle against his siblings in order to earn his role in the family as heir-apparent, whereas all his other siblings who lost the battle were ineffective