The main protagonist of Legal Drug. Above all else, Kazahaya does not want to die - a fact which seems to be linked to a girl from his past named Kei, who has strongly been hinted to be his twin sister. In his thoughts, he has indicated that he and Kei lived a secluded life, effectively trapped on a single property where no other children lived, and also indicates that neither he nor Kei ever finished their schooling even at the elementary level.
At the very start of the series, Kazahaya is found lying in the snow, having apparently run away from his former home and very nearly freezing to death, before being found by Rikuo, who brings him back to the Green Drugstore. Since then, he has always been trying to earn money so that he might live alone, which is the main reason why he accepts the 'extra' jobs offered by Kakei. He has a supernatural power which is something like psychometry in that he can see the "memories" of things or persons when he touches them; he may also possess some empathic ability as he seems capable of absorbing emotions as well as memories, and on at least one occasion has channeled the present visual perspective of another person (Rikuo).
While at times he may seem rather helpless, or at least hopelessly naive, he has many skills and abilities which make him highly capable in certain tasks. Specifically, some of his behaviors and abilities seem remarkably similar to a cat, including a heightened sense of smell and vision, several demonstrations of cat-like agility and speed, and his tendency to look like an angry kitten when upset.
Kazahaya is noted to be 17 at the start of the series, and is smaller, slimmer and has a much more feminine appearance than Rikuo, to the point that he can be accurately described as "pretty." . He gets emotional easily, and frequently plays into Rikuo's hands when teased due to his quick temper.