Why Does Nobody Remember Me in This World?

Humanity once stood on the brink of defeat in a war against four dominant races-angels, demons, undead, and humanoid beasts-until their champion, Sid, defeated the other races' champions and sealed their armies away in four pyramids. Centuries later, Sid has faded into legend, and Kai Sakura Vento is among the many soldiers assigned to guard the pyramids, wary of the ancient foes breaking free. One ordinary day, while relaxing with his friend Jeanne E. Anise, Kai's world is suddenly "overwritten," hurling him into a grim alternate reality where demons have nearly wiped out humanity, forcing the survivors into hiding. Worse, he no longer exists in this world-none of his old friends, not even Jeanne, who now leads the resistance, remember him. Searching for answers in the ruins of his past life, Kai stumbles upon Rinne, a strange girl imprisoned inside one of the pyramids. After mysteriously inheriting Sid's legendary sword, Codeholder, he frees her. Together, they join Jeanne in the fight to liberate humanity from demonic rule. But if Kai hopes to restore his original world, he must first unravel the truth behind the reality-altering event that changed everything.