Shinchou Yuusha: Kono Yuusha ga Ore Tueee Kuse ni Shinchou Sugiru

Synopsis

Ristarte, Mash, and Elulu spend the day enjoying themselves. When they head back to their hotel room, they notice that Seiya is not there. Heading to Ishtar's house, they find a distraught Ariadoa who escorts them to Ishtar's location. Ishtar reveals that Seiya went to the Demon Lord's castle alone. She also reveals that despite his personality and demeanor, Seiya actually cares about them more than he lets on. She then shows Ristarte footage from 100 years ago when Ariadoa previously summoned Seiya to Ixphoria. Back then, Seiya would recklessly fight enemies while unprepared. When the party fought the Demon Lord, it appeared they had killed him. However, he revealed that he had two lives. As a result, he was able to kill the party, including Seiya, Princess Tiana and their unborn child. After watching the footage, Ishtar reveals to Ristarte that she is the reincarnation of Princess Tiana. Despite warnings from Ariadoa and Ishtar, Ristarte insists on finding Seiya and opens a portal to the Demon Lord's castle, taking Mash and Elulu with her to save their friend.

(Source: Wikipedia)