- Kazutaka Muraki is the primary antagonist in Yami no Matsuei. His angelic appearance and characteristics serve to contrast with his brutal nature.
Muraki´s clothing is mainly white. He has white hair and silver right eye. The anither eye is slightly bluer and mechanic. It´s covered by his hair. Muraki also wears glasses.
- Muraki's psychological troubles appear to have begun in childhood with his mother and his half-brother Saki. His half brother was conceived from an affair his father had with one of his patients and Muraki met him when Saki was sixteen, that was when his problems began and how his mother started to have issue's as well because Saki was the result of her husband's betrayal.
Muraki's mother collected dolls, and she is shown as treating him as though he were a doll as well, probably due to the fact that she wanted to keep close to him as Saki came into their lives and Muraki was her only child who she wanted to hold onto. Muraki's love of dolls and his collecting of dolls is a motif throughout the manga and anime, paralleling what he does with real people. In the anime, it is suggested that Saki killed Muraki's parents when they were still children (in the Kyoto arc, Muraki has a flashback of his mother's funeral and sees Saki smirking during the procession) and later tried to kill him in a craze. However, in the manga, it is possible Saki only killed their father, and Muraki describes himself as his mother's murderer, probably because he wanted her to stop treating him like a doll and possibly to set her free from her insanity from having her husband's illegitimate child in her house to remind her of his betrayal. Whatever the circumstances, Saki was shot by one of the family's guards, and Muraki became obsessed with bringing back Saki in order to kill him himself. Thus, Muraki learned of Tsuzuki while researching his grandfather's notes, becoming obsessed with Tsuzuki's body; both carnally and scientifically. In the manga it is clear what Muraki desires, but the anime had to censor such extremes, and so Muraki's advances toward Tsuzuki were shown as hints of sexual harassment.
- Throughout the story, Muraki manipulates souls of the dead, often killing the people himself, in hopes of drawing the attention of the Shinigami, in particular, Tsuzuki.
- Muraki is an expert manipulator, fronting as a good doctor who laments over his inability to save lives, while hiding his private life as a serial killer. As a respected physician, Muraki has many connections throughout Japan among powerful patrons, but in the anime and manga, he is mostly seen in the company of his close friend Oriya and his old teacher, Professor Satomi. Muraki also has a childhood sweetheart by the name of Ukyou, but very little is known about her, other than that she appears to draw evil spirits to her and that her health is poor. During the Kyoto Arc, Muraki discredits his good persona, contrasting himself to Professor Satomi before silencing him. Being a serial killer, Muraki has numerous victims, the most significant of which is Hisoka Kurosaki, whom he raped before placing a curse on him that wiped Hisoka's memory of the event and eventually killed him in the form of a terminal illness. Later, when Hisoka is a shinigami, Muraki forces the boy to recall the night that he cursed him. Throughout both the anime and manga, it's shown that Muraki often refers to Hisoka as a doll.
- Some readers believed that because of his different colored eyes, he may be a guardian of one of the four gates of GenSouKai (see Wakaba Kannuki). However, in the King of Swords arc (volume three in the manga), a scene where Tsuzuki knocks out the fake eye reveals that Muraki's right eye is not real and that it is mechanical. The origin and nature of Muraki's supernatural abilities remain an enigma: he is human (with certain vampiric traits, such as feeding off peoples' life energy [it is theorized that he is an energy vampire]), he is alive (not a Shinigami), yet he raises a dead girl to be a zombie, seals and opens Hisoka's memory by mere touch, controls creature spirits similar to Shikigami, enters Meifu by himself and teleports Tsuzuki to another location. In the finale, Muraki refers to himself as a Descendant of Darkness like Tsuzuki.