The old man was named Gilles de Rais. He had once been the bodyguard and close companion of Joan during her journey as the warrior maiden, but he had lost his life to the French council just before Joan was sentenced to die. He was summoned into this game to serve as Joan's master.
Gilles knew that the gods could not be trusted. Was it not the gods that promised them victory with one hand and then led Joan to the pyre to be burned with the other? No, Gilles refuses to trust the gods for anything ever again. Instead, Gilles would perform a ritual for Joan to live again in this world. He would give her a second chance at life, away from the machinations of the gods.
For the ritual to be successful, Gilles needed to kill a thousand humans and use their blood as a catalyst to allow Joan to regain her former strength. Once the ritual was over, she would have enough strength to destroy all their enemies.