Along with the Dream World and the Human World, the Dark World is one of the three worlds created by the gods. Now it was faced with an unprecedented crisis. The king of the Dark World, Glames, has begun an invasion of the Dream World in order to ensure the survival of his own race...
Yuko is informed of Vecanti's crisis by the demon girl Cham. Once again, she takes the Valis Sword in hand and decides to fight...

More details on the official game page of VALIS III (MEGA DRIVE) ...