From Tokyopop:
Gods and demons wage a neverending battle with the mortal realm as their battlefield. As with most longstanding feuds, the reasons are no longer important--hatred is a way of life. But it is foretold that one would arise who could restore harmony between gods and demons. Enter Raenef...heir to a set of demon royalty, he is hardly courtly material. The demon king assigns Eclipse to be his tutor, to mold Raenef into proper demonic shape. The two begin a journey of discovery and are soon joined by a human knight and a god-blessed priest.
From Mari Lex:
As a demon lord in training, poor Raenef just doesn`t seem to make the cut. With his unbelievable innocence and neivity, not to mention unbearable cuteness dispite trying to look scary, he only agreed to become a demon lord for the free food. Will he ever become a successful demon lord???