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.

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.

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.

Rista, Mash and Elulu enjoy their day of shopping and strolling around town, but when Seiya fails to meet up with them later, they begin to worry. When Rista turns to Ishtar for help locating Seiya, she is met with a surprising revelation.

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.