Lucia no Musou

It has been several hundred years since the Demon King destroyed everything. People have not yet been able to restore their former civilization, and the environment has already charred away all memory of its previous serenity. In the midst of all this, you, who have no memories, wake up. There is only one girl before you. "Do not succumb to the Demon King's curse, and kill him. I don't care what the means are, so please make me a hero - my master."