魔界王子 devils and realist

Seventeen-year-old William Twining takes pride in his lineage as well as his devotion to modern science. When he learns that his family has gone bankrupt, the pompous noble is faced with the reality that he can no longer afford his tuition or the lifestyle he is accustomed to. In a desperate search for valuables in his manor, William discovers a hidden room and accidentally summons the arrogant demon Dantalion, the Grand Duke of Hell.

Apparently, Lucifer—the ruler of Hell—has fallen into a deep slumber. In his absence, only the human "Elector" has power to select a temporary successor, which is the cause of tension among demonkind. Although told that he is the direct descendant of King Solomon and has unshakable authority in the underworld, William refuses to believe it. While denying the existence of magic and the supernatural altogether, the defiant realist fails to recognize that he is at the center of the ongoing battle between Heaven and Hell.

(Source: MAL)