The story is about a young, smart and very intelligent boy, William Twining, the heir of a very rich family. He's very skilled with any kind of subject at the school he attends (he is always at the first place of the tests) , and his dream is to become a very important person, full of money and, above all, rich and trusted by all people.
He is very disappointed when a teacher tells him that his school fees had not been paid, and once he comes back home during holidays, he finds out that Lord Barton (his uncle, the person that dealed with the family issues after that William's parents died), let everything go bankrupt and lost everything, but the house........ and a butler, Kevin Cecil.
William doesn't know what to do to menage to pay the fees before being expelled from the school, and he searches something that could have a valour among things that were left in his home (if there were some XD). In that moment, he loses a single drop of blood and summons a demon, the Duke Dantalion. The demon, was worried about his destiny, because he told William that he had Solomon's soul (Solomon was the emperor of the Demon World) and, that, since in the meanwhile the Emperor was not there, he had the right to elect a king... obviously, the demon wanted William to vote him. The boy, anyway, is a realist, so he doesn't believe in demons and such, and, after seeing that Dantalion didn't had something of a certain value that could help him, he decided to entrust him to the police.
After coming back to the underground place where he summoned Dantalion, William is sucked in a magic circle and ends in a strange place... What's going to happen?