Eijiro is a boisterous and outgoing guy with a fondness for the concept of manliness, often using the terms "manly" and "unmanly" to describe things and people he does or doesn't like. Those who showcase a noble, brave, and/or determined attitude tend to emotionally move him to tears, quickly earning his complete admiration, respect, and friendship. Similarly, he will call out traits that are the opposite of that, such as cowardice and dirty play. He is also a big fan of Crimson Riot, a retro hero that he takes inspiration from, including his own hero name.

Eijiro is very honest and kind-hearted, with All Might praising his heroic spirit. In addition, he seems capable of making friends with most people, as he is one of the few classmates who is friends with both Katsuki Bakugo and Izuku Midoriya. Eijiro is very dedicated to his friends and is even willing to break laws and rules in order to help them, showing regret if he becomes unable to aid in any way. This sometimes leads to Eijiro being very hard on himself.

Eijiro has stated more than once that he does not think very highly of his own Hardening Quirk, thinking that it lacks the flashiness usually found in the Pro Hero scene. In fact, he will get downright offended if he finds someone with a similar Quirk.[1] Eijiro also has concerns about not having a good enough Quirk for hero work, worried that his skills could not compare to the others'. A lot of this self-doubt seems to have come from an incident in Junior High when Eijiro saw Mina Ashido stop an underclassman from being bullied and save some students from a threatening figure.[2][3] Eijiro's friends pointed out that Mina will easily become a Hero due to her outgoing personality and athletic nature. After this, Eijiro thought of himself as dull and boring.[4]

Regardless, in the present, Eijiro is a more confident and hot-blooded fighter, having decided to reinvent himself after being accepted into U.A. High, although he's still not as fiery to the same degree as Katsuki. However, he does not shy away from comparing himself to Katsuki, with Izuku stating that the two have managed to develop a relationship between equals. Because of this, Eijiro is notably one of the few people that Katsuki holds in higher esteem.