Thorn is one of the seven high-ranking members of the Seljild Empire, and one of the most evil among them. She is first encountered by the hero party in Asrafil, where she stabs the protagonist Tristram with her poisonous blade, nearly killing him.
Near the end of the game, she is encountered again atop the Asrafil royal palace, along with fellow Seljild knight Mordred. Thorn is disgusted to see Mordred betray their wicked cause by helping the heroes, and decides to kill them herself by transforming into a large spider demon.
In the original NEC PC-88 and PC-98 versions of the game, a male character named Thorn with a near-identical role is instead featured.