She was always watching.
The humans never noticed her, of course. To them, she was the quiet whisper of a slight breeze; the face of a stranger on a crowded street. She was the things that are never mentioned in the daylight; the soft shadows of night. She was the figure behind the screen.
She was the puppeteer.
She pulled and tugged the gossamer strings of human destiny. She could make mortals do things that they never thought themselves capable of. She could end a thousand lives in an instant.
But most of the time, she just watched.
She watched the humans go about their lives, hearing every single whispered confession. She knew the endless cycle of life and death all too well. She was witness to countless births and deaths. She was witness to love and hate, joy and sorrow, comfort and pain. She watched as blood was spilled, and tears shed. She observed it all with indifference.
She had been there since the beginning. She knew her role -- observe, and only intervene when necessary; pull the strings, but let the mortals decide their fates; remind humans of their mortality, and then slip back into the shadows.
She was never meant to be seen by a mortal.
But she was, and that's how the whole mess was started.