A goddess named Ristarte is given the task of saving a world with an S-ranked difficulty level. She summons her champion, a man named Seiya, whose abilities are off the charts, but whose overly-cautious personality may give her second thoughts.

After Rista and Seiya retreat once again to the Divine Realm, Aria proposes that Seiya train under the tutelage of one of the Gods there. A looming crisis on Gaeabrande compels the pair to return, and seek out companions to aid them in their quest.

Elulu and the others are stunned that she is supposed to offer her life to become the ultimate weapon for defeating the Dragon Lord. The party reluctantly agree to go through with the ceremony, but trouble erupts when they have second thoughts.

A delegation of Roseguard Imperial Knights summons Seiya and the others to a nearby fortress, where a wing of demon houseflies is attacking from the air. Seiya offers his help, but when he butts heads with the knights' leader, things turn ugly.

Mash and Elulu demonstrate some new skills they picked up, and Aria is horrified to learn that Seiya is training with Mitis. Back on Gaeabrande, Rosalie has gone off to challenge the flies alone, and Seiya and company must go to her rescue.

Kilkapul summons a nightmarish reaper to eliminate Seiya and the others, and not even retreating to the Divine Realm is enough to stop its advance. After Mash and Elulu improve their skills, Rista resolves to step up her own game, as well.

In violation of Divine Realm law, Rista opens a portal directly to the location of the final boss fight, where Seiya and the Demon Lord are locked in mortal combat. Seiya resolves himself to make the ultimate sacrifice to defeat the Demon Lord.