Naze Boku no Sekai wo Daremo Oboeteinai no ka?

In the anime Naze Boku no Sekai wo Daremo Oboeteinai no ka?, Kai is a guardian of sealed crypts in a world where humanity emerged victorious from a great war. His existence is upended by a cataclysmic event known as the World Rebirth, which completely rewrites history and reality itself.

Kai awakens in a terrifying alternate timeline where humanity lost the war, his former allies have no memory of him, and he is a ghost in a world he no longer recognizes. This lost hero must now navigate a hostile, unfamiliar landscape, uncovering the mysteries behind the reality shift while fighting to restore balance to a world that has forgotten him.