On Asterra, Rift Gates unleash monsters that threaten humanity. Kael Ardyn, the weakest F-Rank hunter from Valoria, awakens the forbidden Eclipse Core after a near-death battle—a power that absorbs monsters and evolves endlessly, but at the cost of his humanity. As guilds clash and nations vie for supremacy, Kael rises through strength and cunning, earning allies like the S-Rank swordmaster Lyra Selene, and facing rivals and deadly foes, including the masked Harbinger and the Eternal Dragon King Azaryon. From weakest trainee to unstoppable force, Kael must master his evolution, protect those he loves, and decide if becoming a monster is the only way to save Asterra.