In the world of Origone, monsters and humans have learned to coexist. Well, with some setbacks. Humans get the upper hand and control what monsters are reproduced and which are killed off. Only the monsters weaker than humans are allowed to live; and all the high-classed monsters are taken care of by the M.C.S. (Monster Control Squad). Azazel, the youngest M.C.S. member, and Avalane, the alarmingly high - but miserable monster, meet each other and are thrown into a world of strange occurrences.