Why Does Nobody Remember Me in This World?

A hundred years after the great war among five races for supremacy on Earth has ended in victory for humanity under the hero Sid, Kai, who works for the Human Protection Agency, witnesses the world being "overwritten" right before his eyes. The rewritten world is one where humanity has lost the war among the five races due to the absence of the hero Sid.

In this overwritten world (alternate history), Kai meets a colleague from the world before it was overwritten (true history) and learns that he has become an existence forgotten by all mankind.

In a "tomb" that shouldn't exist in the alternate history, Kai meets the mysterious girl Rinne and decides to break this rewritten fate. In a world without heroes, he inherits the hero's sword and martial skills, challenging the mighty enemy races that reign over the earth.