(Taken from the game's text)

A long, long time ago, before human being appeared... there lived a monster named Firebrand in a town of the ghoul realm, Etruria. To become a true warrior, Firebrand trained himself in the Warriors' Training Center every day. But one day...

Morock: "Welcome, Firebrand! Here is the Spectre's Fingernail. You will have the honor of receiving this when recognized as a true warrior. it's time for you to go to the Warriors' Training Center."