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.

After Rista and Seiya return 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.

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.

Following Mash's recovery, Seiya agrees to allow him and Elulu join them on the adventure, but insists that they receive more training first. The pair offer to lead the party to a cave called the Dragons' Den, said to contain an ultimate weapon.

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.