Kazuki is a fairly slim teenager with brown eyes and spiky dark-brown hair with a white streak that goes from the top spike of his hair to the bang that goes in between his eyes. He mostly wears his school uniform which consists of a black unbuttoned jacket with an upward collar and a white and red armband, red shirt and black trousers and trainers.
Kazuki is known for being reckless, often acting before using his brain but usually always means well. He is somewhat goofy at time, often joining in with his friends antics and jokes with them and Tokiko. He has a good nature and will risk his life to save others as seen when he was skewered through his heart by Mita while trying to save Tokiko. He cares about Mahiro and his friends greatly as he fights the Homunculi to protect them, yet chooses not to tell them so they don't get involved.
He has a strong sense of will as he refuses to back down from any opponent no matter how strong they may be. This strong will is fueled even further when he is cheered on by others. On the other hand he gets depressed when he feels he has failed to protect somebody despite doing the best he can to do so and questions his beliefs. After meeting Bravo he decides to hold onto his beliefs until the very end even if it gets him killed.
He has been called a hypocrite on a number of occasions (almost every time by Papillon) with such instances being Kazuki's attempts to stop Koushaku Chouno from becoming a Homunculus and reluctance to destroy him and becoming (albeit against his will) a Victor and thus giving up his humanity.
He is often fascinated by strange or unusual things as he is the only other person to think that Papillon's mask looks cool as well as going along with Captain Bravo's often quirky behavior. He also seems to be fascinated by Tokiko's stomach at the beach as he had never seen it before as well as wanting to touch her scar at the end of the series.