Shuichi appears to have quite a serious and polite personality. However, he is also stated to have a weak personality, and he is abnormally timid when it comes to speaking. He often has negative remarks, frequently blushes and suffers from a cold sweat. With his unsure demeanor, he has a tendency to assume that other people can do things better than him, and he comes across as quite unreliable at first glance. Among the sixteen students, he is a boy who stands out for his submissiveness but also for his level-headedness.

Even though he is a very skilled detective with superior ability and insight, Shuichi lacks self-confidence, as he claims he hasn't accomplished enough to be called a famous detective. He also feels he doesn't deserve his Ultimate title because he only happened to solve a murder case by chance, frequently referring to himself as "kind of a detective", although Kaede says she doesn't believe something like this is possible. Whenever Shuichi feels depressed, he tends to stay in his room and doesn't eat nor shower and at times he can even feel suicidal, but he can get moving with his friends' support.