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 an unperturbed person in the Killing Game. He isn't shaken by murders nor even if he is personally harmed. He often mentions how he refuses to do something "uncool" and doesn't want to show his softer side.

After killing a mafia organization with his own hands, Ryoma 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, and he occasionally gives others a very piercing look as a warning.,

Ryoma 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. However, his younger self 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.