Haunted by the untimely deaths of his mother, little sister, and a childhood friend, listless high schooler Haruomi Io has trouble engaging with anything or anyone. Of course, that doesn't mean others have trouble engaging with him-a fact he discovers to his dismay when he finds himself the target of a trigger-happy group calling themselves the "Seventh Gospel Organization." Having newfound enemies may be rough, but Haruomi's unexpected ally in the form of a demoness calling herself Zilch may turn out to be even more of a handful...Still, there's something to be said for a dose of the supernatural (and more than a few buxom girls) when it comes to casting off the doldrums!

Haruomi awakens to the power of the Ring of Solomon and decides to take up the role of Annihilator in the Seventh Gospel Organization, a society of demon hunters, in order to grant Zilch her wish. Under orders from the organization, Haruomi and Zilch begin a covert investigation to find a new "branch" at Kanmeikan High School, where they're joined by none other than Murohime. What adventures await them there...?!

Having safely completed their infiltration mission, Haruomi and the gang add Hato Mitsukuri to their team, but then 'Goetia,' who has targeted Zilch, sends out the assassin 'The Blue Arrow Marquis' Leraje to attack her!! Zilch is in a hard fight against this 'Branch,' who uses magic arrows, but meanwhile the demon 'Duke' Berith starts closing in on the Seventh Gospel Organization where Haruomi's father is...!? In this slightly lewd and sinful fantasy, the curtain rises on the astonishing 'Goetia' arc!!

(Volume 3)Having safely completed their infiltration mission, Haruomi and the gang add Hato Mitsukuri to their team, but then 'Goetia,' who has targeted Zilch, sends out the assassin 'The Blue Arrow Marquis' Leraje to attack her!! Zilch is in a hard fight against this 'Branch,' who uses magic arrows, but meanwhile the demon 'Duke' Berith starts closing in on the Seventh Gospel Organization where Haruomi's father is...!? In this slightly lewd and sinful fantasy, the curtain rises on the astonishing 'Goetia' arc!!

As Haruomi and the Seventh Gospel Organization arrive to rescue Murohime, Hellenitza has her own designs upon Murohime. What's more, Zilch's bizarre behavior only adds to the chaos. What fate awaits the boys and girls bound by the power of demons in this final volume of Demonizer Zilch?