Meet Harry Potter's older sister, Aster.
She's sixteen years old, and perhaps one of the funniest, sweetest, kindest people you'll ever meet.
She's the spitting image of her mother.
Which gets to Severus Snape every time he sees her. Which makes him even colder to her than he his to the rest of his students, even poor Neville Longbottom who blows up his classroom nearly every time he sets foot in it. Aster just brushes it off, and continues to be kind and civil to her professor, which makes it so much harder for him to hate her.
This is the year that Dumbledore requests she becomes a part of the order, and a spy.
She becomes the one thing in the world she actually hates.
A Death Eater.
Story starts in Goblet of Fire.
Based off my one-shot: "Always."