The realm Clyde was a part of started suffering from invasions twenty years before the novel's start. Tremors caused from hordes of beast or a singular strong beast, is how the world has determined classification of threats. Additionally, humans began to awaken with new abilities around the same time as the invasions.
Threat level severity (least to most)
Ash
Ember
Flame
Inferno
Volcanic
Cataclysmic
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Abilities:
Once a person awakens they are usually granted an affinity to an element, in rare circumstances a person might get something unique only to them.
Through intensive training and mastery of abilities a person can undergo a second awakening. A persons strength is doubled in addition to refined ability usage.