One of my alltime favourite animes.
Plot: The story takes place in a fictional world called Arcadia, where life-draining monsters called Thanatos plague the populace. The only ones who have the power to exterminate these creatures are Purifiers, but only a few exist. One day, Angelique, who is just a presumably normal girl attending school, is visited by Nyx, a rich gentleman as well as a Purifier, who created an organization of Purifiers dedicated to exterminating Thanatos. Nyx is interested in the potential power she possesses and invites her to join his organization, but she refuses since she wants to become a doctor, like her father. However, when her school is later attacked by Thanatos, she ends up activating her powers in her wanting to protect those in danger. After purifying the creature, she finds out she has a unique purifying power, and that she is the one that has been foretold in legends, the "Queen's Egg". It is then that her journey begins, and she becomes the only female Purifier in the world.