Why Does Nobody Remember Me in This World? - S01

In a war against four overpowered races, angels, demons, undeads, and humanoid beasts, humanity survived only because of its champion Sid, who defeated the other races' champions and sealed their armies inside four pyramids. Now, in an age where Sid has faded into legend, Kai Sakura Vento is just one of many conscripts assigned to watch over the pyramids, fearing that these old enemies might one day break free. During a peaceful day spent with his friend Jeanne E. Anise, the world is suddenly "overwritten," and Kai is transported to an alternate reality where humanity has been nearly wiped out by the demons and forced into hiding. Worse still, his existence has been erased from this world. All his friends, including Jeanne, who leads the local resistance in this reality, have forgotten him. While investigating what remains of his former world, Kai meets Rinne, a mysterious young woman trapped inside a pyramid. After mysteriously inheriting Sid's legendary sword, Codeholder, Kai manages to free her from her imprisonment. Determined to fix this reality, Kai joins forces with Rinne and Jeanne to free humanity from demonic rule. But if this brave soldier wants any chance of returning to his original world, he must first uncover what caused reality to be altered in the first place.