Angel Sanctuary (Tenshi kinryoku) (2000)

Setsuna, a High School student, not only has to deal with bullies and more then appropiate feelings for his own sister, but also must come to terms with the fact that he is the reincarnation of the Organic Angel Alexiel who rebelled against God. Being thrust into a world he never knew existed he must believe that angels and demons exist for the sake of Heaven, Earth and even Hell.