After losing his memory and being hired to search a dungeon for an ancient artifact by the demon Ignis, Kona ends up falling into a hole leading into a hidden room where he finds a powerful demon sealed away and ends up opening the seal. The demon unlocks his lost memory, unlocking the truth to Kona's past where he was abandoned by his country and left to die. He makes a deal with the demon to obtain its power to escape the dungeon and seek revenge. For its power all he has to do is combine souls with it until he can find a body powerful enough for it to take over. With the demon's power now he begins his journey for revenge and become an overlord to rule the world.