The title involves the twin Amatsu sisters, Ai (天津亜衣) and Mai (天津麻衣), students at the Tenjin Girls High School who become virgin priestesses that must watch over the boy, Onimaru (鬼麿), a distant relative of theirs. It becomes his choice to make the world a hellhole of debauchery or to keep as it is. Onimaru (鬼麿) is the descendant of a line of men whose founder was betrayed by the Japanese government, and whose spirit seeks revenge by making Onimaru a sexually depraved demon king. The founder is the younger brother to the twin sisters. The three of them are the result of a union between a fisherman and an Angel (Tennyo) of the Buddhist tradition.