Makai Ouji: Devils and Realist

Plot
After his uncle's business fails, William Twining, an intelligent young noble, finds himself in a dire financial situation. With no funds for his school tuition, he searches his house until he comes upon the basement. There, he accidentally summons Dantalion, who recognizes William as a descendant of Solomon. He also realizes that William is the Elector—the individual that will choose a substitute ruler for when the Emperor of Hell, Lucifer, rests.

From that moment on, William's life is irrevocably interwoven with the supernatural world as other demonic candidates for substitute king vie for his nomination and Heaven attempts to retrieve his soul.