In Liturgical Year 526, sorcery has spread throughout the land, but few are aware of a rival practice called "magic." One day, a half-man, half-beast mercenary who has found himself on the run encounters a beautiful witch known only as “Zero.” Zero makes him an offer: if he escorts her on the search for her stolen grimoire, she will help him gain a human form. Despite his hatred for witches, the nameless mercenary accompanies Zero and guards her as she sets out to reclaim a book that has the power to destroy the world.