The main character of the series. Though and a genius detective, is not particularly interested in going out and finding wrongs to right. Rather, it is his erstwhile partner Kana who drags him into getting involved. An introvert, he is well-known for his intelligence, although he is not particularly popular.
Sou is introduced when Kana Mizuhara rescues him from an irate customer at a video arcade. He then assists Kana's father in finding a murderer. After that, he and Kana are often seen together, although she denies they are going out.
Sou's past is a mystery, and he appears to be a sort of polymath with a wide range of knowledge. What is known is that he graduated from MIT in the United States and was planning on continuing to graduate school, but then decided to drop out for unknown reasons and came to join Kana's high school. While highly intelligent, Sou is often seen being amused by such simple things as snowflakes, suggesting he did not have an ordinary childhood. During cases, he becomes even more quiet and it is sometimes hinted that, in addition to Kana's prompting, he only solves cases for his own reasons.
Sou is also often the unfortunate recipient of Kana's violent tendencies, as he is often bopped on the head for reasons ranging from asking an embarrassing question in public to accidentally looking up her shorts. Despite this, and despite complaining whenever Kana drags him somewhere against his will, he demonstrates concern for her, often taking her along whenever he goes out of town. He also doesn't mind it when people call Kana his girlfriend.
Besides being a genius, Sou is also wealthy and can speak in a number of languages including French. He is seen as having interest in archeology and biology. He has a younger sister named Yuu who is a genius with all languages; however she is so spacy that she often forgets what she's supposed to be doing.