Kozume is shown to be very lax and laid back. He has hardly ever lost his cool, and he usually never gets excited about anything (with the exception of Hinata and video games). He is quiet and reserved, and does not voice his opinions often, since he is afraid of how others would think of them. It had been noted that he wasn't the type who could make friends easily, and his only friend back then had been Tetsurou Kuroo, his next door neighbor. Despite his modest personality, he is actually quite skilled in volleyball, with his extraordinary game sense and technique, which makes up for his power, speed, and stamina.