Premieres sometime in 2024. English article for more info and character visuals. Synopsis from AniList:
Why does no one remembers the true world...!"
The era when the great race of the five tribes competing for hegemony on the ground ended with the victory of mankind led by hero Sid. However, that world was suddenly "overwritten" in front of a boy Kai. In the rewritten world, Kai saw the scene where humans lost to the five tribal wars because of the absence of hero Sid—here dragons and demons dominate the ground, and Kai is a forgotten existence from all human beings. However, after encountering the mysterious girl Rinne, Kai decides to break this rewritten destiny. In a world without heroes, he inherits the hero's sword and martial art and challenges the mighty enemy races who reign.
I speak some Japanese, and I read it as “Why does nobody remember my world/Why doesn’t anybody remember my world?”
It’s definitely saying the world is what was forgotten.