Junketsu no Maria

The story follows Maria, the most powerful witch who lives during the Hundred Years' War in France. She despises war, so she obstructs battles with her strong magical powers. Her meddling with her succubus Artemis and incubus Priapos has caught the attention of the heavens, and so the Archangel Michael issues an edict. When Maria loses her virginity, she will also lose her magical powers. A beautiful angel named Ezekiel is supposed to watch Maria and make sure the witch does not use magic in front of people, but Maria continues to use magic anyways.

(Source: Anime News Network)