エリス・エクシリア

A valkyrie (a type of angel) dispatched from the heavens to smite the Demon King. With her strong sense of responsibility and her dedication to proper decorum, she comes across as a genuine honor student. She is easily tricked by semantics, which Tsuguhiko often uses to his advantage, having plenty of opportunities to tease her due to her lack of knowledge about the human world. Tsuguhiko’s dark powers cause her to become partially human and require both food and sleep, after which she develops an enormous appetite. Completely clueless when it comes to sex, she gradually becomes educated in these matters through her experiences with Tsuguhiko. To watch over him in his everyday life, she begins attending his school and becomes the Student Council President. [From MangaGamer]