The manga's primary antagonist, Kazuo Kiriyama is a ruthless killer, who is also a savant with no feelings of remorse. He also possesses a genius level I.Q., mastering things such as playing the violin in minutes, and has an uncanny ability to adapt to situations quickly. His starting weapon is a Ingram MAC-10 Uzi. Kazuo has AB-type blood. The characters in Kazuo's given name mean "peace" and "male," respectively. The characters in his family name mean "mist" and "mountain." In the novel and manga, it's implied that he is an illegitimately born child due to maternal infidelity. After killing his gang in the novel, he touches his left temple due to some elusive feeling he infrequently has. Kazuo states that since the doctor who operated on him died and, as he puts it, "his real father" dying of complication, he has no one to question about this. In the manga, Kazuo is much like what the novel depicted, mercilessly killing his classmates with neither hesitation nor regret. Some fans have also noted that there are physical similarities between Kazuo and Hiroki in the manga. The two are near the same height, both looking alike as children and as teenagers (before Kazuo slicks back his hair), even acquiring the same eye injury by the same weapon. They are also both highly trained martial artists, Kazuo having the edge over Hiroki in a straight fight. One of the more notable differences from the novel version is that Kazuo's brain damage is caused by a car crash in his childhood rather than in utero, an event made clear in volume 14 in a sequence where a wounded Kazuo (shot from an angle by Noriko Nakagawa that eventually hit the damaged part of his brain) flashes back to his earlier (and happier) years. Here it is also hinted that Kazuo is colorblind, when he expresses shock at colour and wishes for it to "all go back to grey" (although this conflicts with his earlier observation of "They all bleed red"). The manga depicts Kazuo as a near perfect genius, from his incredible talents when he was a child to his wide range of knowledge as a junior high student. He appears reading books about human anatomy and martial arts, and has the ability to quickly grasp anything not yet familiar to him. An example of which being when Kazuo appears to learn Judo in the course of a martial arts lesson, in order to fight his teacher who he then defeats by pulling out his eye.
