Kazutaka Muraki is the main antagonist in Yami no Matsuei. His angelic looks and demeanor sharply contrast with his brutal nature. Psychological issues seem to have plagued Muraki since childhood, stemming from his relationship with his mother and half-brother Saki. His mother, a doll collector, treated Muraki as if he were one of her dolls. This fascination with dolls becomes a recurring theme throughout the manga and anime, reflecting how Muraki treats real people. In the anime, it's suggested that Saki killed Muraki's parents when they were children and also tried to kill Muraki. However, the manga leaves Saki's role ambiguous beyond disrupting Muraki's childhood, while Muraki claims he murdered his own mother.
Regardless of the specifics, Saki was shot by a family guard, and this led Muraki to become obsessed with bringing Saki back to life to kill him himself. Consequently, Muraki aims to use Tsuzuki's body for this purpose. This subplot is prominent in the last three episodes of the anime and volumes seven and eight of the manga.
Muraki is a master manipulator, posing as a compassionate doctor who laments his inability to save lives, while concealing his true identity as a serial killer. He contrasts himself with Professor Satomi during the Kyoto Arc in episode 12. As a serial killer, Muraki has many victims, notably Hisoka Kurosaki. At age thirteen, Hisoka was stripped naked and cursed by Muraki. The curse mimicked a terminal illness, leading to Hisoka's death after three years in the hospital. Later, as a shinigami, Hisoka is forced to recall the night of the curse by Muraki.
Throughout the story, Muraki manipulates the souls of the dead, often killing them himself, to attract the attention of the Shinigami, particularly Tsuzuki. Obsessed with Tsuzuki's body both sexually and scientifically, Muraki's desires are more explicit in the manga, whereas the anime censors these extremes, hinting at sexual harassment instead. It is later revealed in the anime that Muraki seeks Tsuzuki's body to revive his half-brother.
A respected physician, Muraki has numerous influential connections across Japan. He is mostly seen with close friend Oriya and former teacher Professor Satomi. Muraki also has a childhood sweetheart named Ukyou, about whom little is known other than her ability to attract evil spirits and her poor health.
Some readers speculated that Muraki, due to his differently colored eyes, might be a guardian of GenSouKai’s four gates. However, in the King of Swords arc, Tsuzuki knocks out Muraki's fake eye, revealing it to be mechanical. The origin and nature of Muraki's supernatural abilities remain mysterious: though human and alive, he raises the dead, seals and unseals memories with touch, controls spirits akin to Shikigami, enters Meifu on his own, and teleports others.
