Monster Lord Cassandra

She comes from another world and tells a story about how she devoured her world: She started by devouring the hero Luka, before using the power she acquired to move on toward devouring Alice and then the Heavenly Knights. She then took her time devouring Ilias, before eventually devouring her whole world's inhabitants, and becoming "The Monster Lord who devoured the world." This shocks Alice and Ilias, and she challenges the party as she needs a new world to live in. Once defeated, she forces her way into the party out of denial after her loss.