Katsuki is a crude, arrogant, short-tempered, and aggressive person, especially at the beginning of the series. Katsuki tends to come off as unheroic, if not downright villainous for those not familiar with him. This problematic behavior goes all the way back to his early childhood days when he was known to bully a young, Quirkless, Izuku Midoriya. He shows hostility towards Izuku, mainly because of his former Quirkless status.

However, after being accepted into U.A. and experiencing several personal defeats, one of them even coming from Izuku, Katsuki has gradually changed into a less antagonistic person, albeit still retaining a lot of his unpleasant traits. While often portrayed negatively, Katsuki's fierce character and competitive drive have actually granted him an important role among Class 1-A, as a sort of inspirational mood-maker.