Izuku is a very timid, reserved, and polite boy, frequently overreacting to abnormal situations with exaggerated expressions. Due to yeаrs of being looked down on by Katsuki for lacking a Quirk, he is initially portrayed as insecure, tearful, vulnerable, and non-expressive. These traits are especially present around Katsuki, who also constantly harangued him for his aspirations to become a hero. However, after being accepted into U.A., making new friends, and facing Katsuki during the Battle Trial Arc, Izuku gradually matures into a more confident and brave person who's always eager to prove his worth as a hero, eventually developing strong leadership skills, which combined with his passion and strategic abilities, have turned him into a central figure within Class 1-A alongside Katsuki.[4]

Izuku is a quite diligent and strong-willed student, being extremely (and sometimes scarily) enthusiastic about topics related to heroes. His dream drives him to write down notes about everything he learns in regards to heroes' Quirks and fighting capabilities. Thanks to this practice, Izuku has developed a great analytical mind and can form complex battle plans in a few seconds, factoring in the best ways he can utilize the Quirks of allies and enemies alike for his own advantage.

Izuku externalizes his observations through endless mumbling, a habit that annoys or creeps out his peers. Izuku often writes down his observations in a variety of notebooks he titles as Hero Analysis for the Future, checking on them regularly during school activities or at night.

Izuku is caring and emotional, never hesitating to help or rescue someone in danger, even if he knows that he might not be strong or qualified enough to do it. Often, he does this on instinct, taking a more careless approach than the usual overthinking he goes through and putting himself in peril in order to protect someone.