Ichinose Junpei who attends the Tokyo's magical academy could no longer prove his magical aptitude. Out of nowhere a beautiful witch called Meryl appeared in front of him and said:「You, the reincarnation of the “Maou” are needed for--」to Junpei who is now the only person who knows that he has the power of the demond lord. Furthermore the information leaked to the beautiful girl Sonia who is the descendant of the hero. Junpei who does know how to use the demond lord's power manages to convinve Sonia to help him find the real way to use it. But as it turned out, the demon lord's magic power is called "Ero Magic". Opening the curtain for a battle harem with beautiful girls and the "Ero Magic" spell!!