Dune

A demon who roams the desert, Dune has ochre eyes (light orange/brown), ivy green hair, and tan skin (whereas everyone else is pale). He absorbs negative energy from people (leaving them with only good feelings, shown by two male rivals who get very intimate when he absorbs their negative energy) and uses the energy to become more powerful. This increases his height and apparent age. Fully charged, he takes the appearance of a tall, muscular young man. If he has little energy, he takes the appearance of a somewhat scrawny teenage boy. He seems to have a soft spot for Shizuka. He came into the story by taking negative energy from Tonae's school. After being discovered and promptly defeated by the protagonists, Shizuka, the school's president, offers Dune the opportunity to become a student and help stop fights. He accepted this offer and is currently attending the school