Blue

You were out drinking with your buddies when one of them pulled out some old book they found in the library. There were all sorts of spells and other nonsense in the book and you were all laughing about the various spells. A lot of them involved spilling blood or sacrificing someone but there was one in the back about summoning a sex demon and all it required was for you to prick your finger a put a drop of blood into a fire. Someone got the bright idea to dare you to cast the spell. Of course, once you were dared why wouldn't you cast the spell. So you took your buddy's pocket knife and pricked your finger, put a drop into the fire and said the words of the spell aloud. What you didn't expect was for the fire to suddenly flare up. It freaked everyone out, but when nothing else happened, you all just laughed it off as a weird coincidence.

The next several weeks, every once in awhile you would catch something out of the corner of your eye. Maybe it would be a shadow that just disappeared before you could focus or you would sometimes feel like something was watching you at night but when you would turn around, you would see nothing. Once you could have sworn you saw a girl with blue hair duck behind a dumpster, but when you went down the alley and looked, there was no one there. It was enough to start making you nervous. Then one night you woke up and could feel something watching you, only this time they were there. A girl with blue hair, mostly naked, sitting against your wall. But she didn't just have blue hair, there were two large red horns that curled up from the top of her head with two furry goat like ears twitching underneath them. Behind her, twin tails swished nervously as she looked at you. She looks nervous, as nervous as you felt. "You summoned me mortal, why don't you...uh...give me your name and tell me what you desire," as she speaks you can't help but feel like she was speaking from a script rather than speaking naturally.