Arion, the last of the Monster Sealer class, is entrusted with the task of sealing 100 Greater Immortal Monsters whose very existence disrupts the balance of mana in the world. To gain the strength necessary to face these creatures, Arion must locate the hidden tombs of past Monster Sealers and inherit their legacies. However, his journey is fraught with danger as some humans stand on his way, seeking to exploit the immortal monsters for their own gain.