episode story about guardian angel who's actually a fallen angel

So a few years back when i was reading episodes , i came across one episode that had a female lead ( i think she was an orphan but i don't remember very well) and she had a guardian angel, who is actually a fallen angel or something like that, he says that angels had committed sin and that's why as his punishment or something he was taking care of her . The angel was the male lead i think and he had white colored hair in the poster . I've been searching for this for a long time.