The Monster Classification is a ranking system that defines the level of power for all ayashi. Certain attributes including physical strength, level of yōki (demonic energy), and other latent talents contribute to an individual's rank, though no criteria has defined the level of power for each category. The system largely sets on individual basis, however certain Ayashi races are presumed to have all members in a single class level. Only 2 categories have been mentioned: S class monsters and the A class monsters.