Underneath The DressThe Muraki we see now.
Muraki's childhood until early adulthood and psychological traumas played a great role in honing the Muraki we know now; the main antagonist of the series. Aside from the fact that Muraki is an enigma, his true nature is quite horrifying as well. Throughout the story, he has been manipulating the souls of the dead to appear as a good, respected doctor, so no one could get in the way of his plans. Behind this deceitful facade, Muraki is actually a serial killer; and tends to think of human life as something that can simply be thrown away. He does kill people without any particular reason just to draw the attention of the Shinigami, particularly Tsuzuki.
But his ultimate motive is to find a way to resurrect Saki, his older half-brother just so he could kill him himself. And in order to do it, he wishes to use Tsuzuki; a person who was able to survive for eight years with no food or water and barely any sleep, whom his grandfather had researched upon. This is the main reason why he is determined to win Tsuzuki over, and will go to all lengths to ensure that, including kidnapping and murdering. And since he also lusts for Tsuzuki, the murders are also a way to force Tsuzuki to unwillingly go on a date with him.
Sadistic and SeductiveI've gone mad...
What is a story-line without a twisted character? Muraki fits several criterias for Antisocial Personality Disorder in any way. He shows an astonishing lack of remorse for the crimes he has done, has no sympathy for any of his victims and shows a seemingly reckless disregard for his own safety, and that of others. With an obviously inflated sense of his own self-worth, Muraki is also arrogant and vain.
Muraki is also charismatic if it's still not obvious when he's being admired by the nurses and students in the Kyoto arc. It is also if it's not by this charisma, it might be difficult to pull off his strings perfectly.
While everything seems natural with Muraki, a part of his charisma radiates a seductive menace. With this nature, he is often seen blatantly invading Tsuzuki's physical space more than once both in the anime and the manga. Although the menace is much more subtle in the manga, Muraki's behavior still far stretches the boundaries of what could be considered inappropriate.