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 than draws Sou into cases.
She first encounters Sou when she rescues him from being attacked by a bully at a video arcade. She is warned by her close friend that Sou is mysterious (having apparently come to their high school after leaving MIT) and she should probably leave him alone. Shortly thereafter, her friend learns her father was murdered, leading Kana to drag Sou along for support. Her father, Detective Mizuhara, is in charge of the case and with Sou's help arrests the murderer.
Since then, the two have been nearly inseparable, in that Kana drags Sou almost wherever she goes. She categorically denies that the two 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 little she learns often either impresses her or makes her unhappy at how much Sou's been through.
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. She is also infamous for her violent tendencies, showing no mercy to anyone who suggests there is something more to her and Sou than friendship.