Tsukikage Ars Magika -Fukagyaku Shin'iki no Shoujo-tachi-

The protagonist is a student commuting to Yasaka academy. However, he isn't a normal human, he's actually somebody who can steal life force from other people. He only transfers to this school because it's more convenient to do his work. One day, a new student transfers to his class. Due to her different essence, he notices that she is some kind of exorcist. And thus, he is excited by the higher-quality life energy, something that he hasn't tasted in a long time.