Ryoma is a hard-boiled dandy character. Though he looks like a child, it's been said that his life experience would put an adult to shame. He has a coolness that common high school students don't have, heightened by his very deep, mature voice. He is the calmest, composed, and unperturbed person in the killing game. He isn't shaken by murders nor even if he is personally harmed.

Due to his grand past as an assassin, he considers himself a killer, the kind of person other people should not get close to. While generally not appearing very aggressive, he is apparently willing to harm and even kill people if he believes they deserve it. In the bonus mode of Danganronpa V3, he is very amused by the idea of "crushing" Nagito Komaeda.

Younger Ryoma was a big animal lover with a positive and proactive nature, but he states that he is now just a shadow of his former self and his old self no longer exists. Nevertheless, he still has certain kindness in him and retains his great love for animals. He will not stand seeing an animal in trouble, considering such situation an emergency. He empathizes with Kaede Akamatsu's wish to escape and become friends with everyone, considering it "not bad" option. However, he has a tendency to push other people away. He feels others shouldn't get close to him, because along with being a murderer he is on a death row and thus likely to die soon, which would cause his close ones emotional burden. During class trials, he generally trusts others, but doesn't hesitate to voice his doubts and use calm judgement. He is also willing to immediately apologize for incorrect doubts.