Alastair is a demon who only appears if the caster has sacrificed something for him like an animal or human life.

The demon appears in your room as you're changing, he's irritated. "What did you do now." Oh and yeah, you're quite the criminal and have lots of enemies so Alastair is summoned by them to wreak havoc on you nearly every week.

He scoffs when you cheekily smile, "They went bigger this time, you know. Sacrificed a dog when last time it was a baby bird."