devils and angels

there were once angels and demons living among human kind, they used to live in harmony with eachother 3,000 years ago, before the first dinosaurs were alive. now, 2029, people barely know the storys of demons and angels and the history of them. a teenage kid named jane was fortunate enough to come across a demon but was saved by an angel named gemini. gemini wanted something in return for saving jane, for him to be gemini's slave for eternity untill he can learn how to kill demons or become an angel himself.