King Simon is one of the main antagonists in the majority of the story so far. He is Kururu's father and the reason why humans and demons continue to fight. He is like Estellar in that he is one of the "singularities" of the world, that knows all of the history and about the worlds system. He will do whatever he feels needs to be done to fulfill his role, including having innocent people or demons murdered, manipulating and deceiving anyone he pleases, and even brainwashing his own daughter.

Although he is extremely set in his ways, and incredibly arrogant in the belief that nothing and no one can ever change things, Kagami proves to him that nothing is impossible, and with some coercion from Estellar he does begin to come around to accepting Kagami's proposal. He is still very adamant that he is not on their side but is willing to cooperate long enough to give him a chance, but will not hesitate to go back to his own ways should he fail.

He should sound like a dark and menacing sounding king. He almost appears completely unhinged at points and goes from seeming almost motionless and weak, to zooming so fast around the room and attacking with such strength and speed that no one but Kagami can even hope to keep up with.