The protagonist of the tale is Oz Vessalius, a wealthy duchy's heir. When he is cast into the Abyss, a jail for criminals who are alleged to have committed unforgivable sins, as part of the coming-of-age ceremony, his existence is entirely turned upside down. He is assisted in escaping by a Chain creature there, represented by Alice, a blood-stained rabbit. He thus joins a secret organization named Pandora.
