Naze Boku no Sekai wo Daremo Oboeteinai no ka?

Why Does Nobody Remember Me in This World? unfolds in a world where humanity once survived a devastating war against four superior races—angels, demons, undeads, and humanoid beasts—only because the hero Sid defeated their champions and sealed their armies inside four pyramids. In the present day, Kai Sakura Vento is one of the soldiers assigned to watch those prisons, alongside his friend Jeanne E. Anise, so the old enemies never return. Everything changes when the world is abruptly overwritten. Kai wakes up in a darker alternate reality where humanity has been pushed into hiding by the demons, and even worse, everyone he knew has forgotten he ever existed. Jeanne now leads the local resistance in this world instead of standing beside him, while the ordinary life Kai remembers has vanished. As he searches for answers, Kai discovers a mysterious young woman named Rinne trapped inside one of the pyramids. After inheriting Sid's legendary sword, Codeholder, he frees her and joins forces with Rinne and Jeanne to challenge demonic rule. To restore his own world and uncover the cause behind the alteration of reality, Kai must follow the trail left by a legend that history itself seems determined to erase.