Sekai no Owari no Sekairoku

A brief description of the mangaSekai no Owari no Sekairoku:

The valuable treasure, the “Encore” which was left by the legendary Brave Hero Elline, has the recording of the end of the world and the reincarnation of the world. The countries and parties all over the world are searching for the location of its whereabouts; the age to fight for the Encore. The boy called Ren who wants to become a MASTERKnight has no talent in wielding swords despite looking exactly like the Brave Hero Elline, he has been having a lifestyle where people taunts him as the “Fake Brave Hero”.

The one that appears in front of him is the legendary Dragon-Princess Krische, who had awoken from her seal. She mistook Ren for Elline. Though she gets disappointed since he simply looked like him, she later finds out a hidden potential in him. And she invites him to the journey to find the Encore together with the Archangel Phia and the Demon-Lord Elise that saved the world before. “Do you want to come with us?”