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.

Chaos Machina proves too much for Seiya and Rista, and they retreat back to the Unified Divine Realm. However, when Machina takes the entire town hostage, the pressure is on to come up with a way to stop her before more people get hurt.

With a massive undead army approaching, Seiya dismisses any assistance from Mash, who does not take kindly to the snub. However, when Mash later turns up missing, it is up to Seiya and the others to rescue him from the enemy's clutches.

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.

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.