Throughout the seventeenth and eighteenth centuries, exotic tales of conversion and martyrdom set in Japan played out upon the Jesuit stages of Europe. It is in this way that Japan's Christian Century (1549-1639) endured in the Jesuit mind as a source of spiritual and creative inspiration. The development of the "Japanese genre" in the acted and musical dramas of the historical Society of Jesus is a scarcely travelled road of research. In exploring this unique performance tradition, the article presents an analysis of the only known example of an oratorio based on a solely Japanese theme: La conversione alla santa fede del re di Bungo giaponese (1703). The article addresses the oratorio's literary genealogy in order to identify the librettist's didactic intention. In so doing, the representation of theological disputations between the Jesuits and the various sects of Buddhist priests in the mid-sixteenth century is reconstructed and examined.