If called upon by a ritual -
most demonic beings follow the call.
And on the other side of the magic stands -
a human being, in a trance.
Their wish will be heard and fulfilled for a price -
in exchange for a soul, demons play nice.

When a desperate person calls out into the void - what happens when the void stares back?
Lily Potter is a strong woman, but in the face of almost certain death, even someone like her can come to the conclusion to fight fire with fire, and call upon a demon to fight the inhuman Dark Lord tearing down her home.

Once called, Nightmare takes on Harry as her child... this doesn't bode well for the sanity of everyone else involved, especially once she finds a very special letter addressed at herself years later.

Disclaimer:
The Nightmare in this story is a (far) future version of the Nightmare found in my other story.
The 'Sex' tag is for roughly two sentences implying it in a chapter near the middle (hence this story's rating).
The 'Death' tag is for, well, the death of Harry's parents.

Image by Feynna