Main Characters
The main character of the series. Though Sou is a genius with a keen mind and sharp observation skills like a detective, he is not particularly interested in going out and finding wrongs to right. Rather, it is his classmate Kana who drags him into getting involved. An introvert, he is well-known for his intelligence, although he is not particularly popular.
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, but for unknown reasons he decided to come to Japan and join Kana's high school.
- Bespectacled Cutie: Sou wears glasses in early part of the series, and Kana's girl classmates note that Sou, though often act like a weirdo, is a good looking person.
- Beware the Nice Ones: If someone hurt people Sou cares about, such as Kana, Sou will surely enact payback on that person.
- Break the Cutie: Poor Sou, witnessing the bitterness of real world at 10 years old...
- Brutally Honest: In the first chapter, Sou bluntly tells his opponent that he defeats in an arcade game that they sucks, which understandably angers the opponent.
- Cerebus Retcon: In early parts of the series, Sou often refuses to help with the investigations or other kind of errands and only do so after Kana strong-armed him, which serves as a Running Gag for quite a while. Later in Volume 10 story "In the Hand of the Witch", it is revealed that Sou had witnessed one of his few friends in America getting shot after Sou gave a help in a difficult case. The incident makes Sou bitterly believe that his help will only burden others.
- Clear My Name: Defied. In "The Rainbow Mirror", Sou does not have any need to clear his name despite being one of the prime suspects for incidents involving people related to Annie Craner case and still wanders around Massachusets. Sou admittedly only wants to find out who sent him the mysterious halloween post card, and once he correctly deduces that Annie is perhaps still alive, he wants to meet her as well.
- The Determinator: Once Sou sets his mind on something, he will see to get it done. Heck, after he finds the mysterious halloween post card, he travels to Massachusets by himself to discover who is the sender and why they sent it to him.
- Intelligence Equals Isolation: In the past, Sou got bullied for being a Teen Genius Grade Skipper from Japan.
- It's All My Fault / My Greatest Failure: Sou thinks that him not being able to do anything when Annie got shot was his fault, and that event still haunts him even after he left MIT and goes to Japanese high school.
Kana is a spirited, tomboy who excels in virtually every sport she attempts. Brave, athletic and rather pretty, she has also been described as having a heart "big enough to float a planet". It is her willingness to help others that draws Sou into cases.
Kana is a popular student, and she is often seen in a leadership role. She practices judo and kendou, the former skill often coming in handy when attempting to defend herself or Sou and apprehending suspects.
Kana categorically denies that she and Sou are dating, but there have been many hints in the manga that she is slowly developing feelings for him. The fact that she knows so little about his past bothers her greatly, and she often tries to find out more about him, going so far as to secretly follow him after school. What she eventually learns about Sou either impresses her or makes her unhappy at how much Sou's been through.
- Action Girl: Kana is The Ace of her school's kendo club, and is quite good at hand to hand fight.
- Fiery Redhead: She has red hair and is hotheaded.
- Nice Girl: Despite her violent tendencies (especially toward those who suggest that she is dating Sou), she is still one of the nicest individuals in the story, and her desire to help others in need is what often draws Sou into cases. Most times, she volunteers to get informations herself, then she provides her findings to Sou to analyze.
- She Cleans Up Nicely: Mostly wears either casual clothes or school uniform (or kendo outfit when she is practicing), but she ocassionally wears dress when she and Sou are attending formal events. One time when Sou sees Kana wearing a dress for the, he is seen flustered.
Supporting Characters
Kana's father. A gruff, unshaven police detective, he is introduced as the chief investigator of the murder of Kana's friend's father. After Sou helped him unmasking the murderer, Detective Mizuhara develops a healthy respect for Sou's abilities.Detective Mizuhara is known for his straightforward no-nonsese yet fair methods when dealing with suspects, and for refusing promotions to join "top siders" in Tokyo Metropolitan Police Department several times.
- By-the-Book Cop / Reasonable Authority Figure: On "Imperfect Closed Room", Detective Mizuhara insists to look for more clues at the crime scene because the situation still shows reasonable doubt. He ends up discovering blood stains covered by several drums, obviously done by someone intended to forge evidence.
- Face of a Thug: With his tall imposing figure, his unshaven face, and his Perpetual Frowner expression, no one blames you for thinking he might be a Dirty Cop or even a Killer Cop upon the first time you see him. He isn't, fortunately.
- Police Are Useless: Averted, Detective Mizuhara is amongst the most competent and disciplined investigators in the series.
- Smoking Is Cool: He often smokes cigarretes while performing investigations.
An old friend of Sou Touma from MIT, Loki a highly intelligent individual (particularly in math) just like Sou. He and Sou are like brothers, and he often teases the younger boy.
- Establishing Character Moment: His first appearance in the manga involves him trying to explain a complicated college-level math formula in English to Japanese high school students.
- Et Tu, Brute?: Saying Loki is angry or disappointed upon knowing that Eva Sukta was the one who destroyed Sou's thesis in the past is a major understatement. Loki ends up forgiving Eva because Sou asks him to.
- Friendly Rival: He was this to Sou in MIT, and still considers Sou a friend even after the latter left United States.
- Intelligence Equals Isolation: Loki used to be lonely before meeting Sou in MIT Mathematic Department as fellow students and formed a Friendly Rival relationship with him.
- Meaningful Name: His nickname Loki is obviously inspired by Loki, the god of mischief from Norse mythology. Loki enjoys riddles, pranks and games like his namesake.
- Smoking Is Cool: He smokes and he is a cool math prodigy.
