Airis is Scott's sister, but they haven't seen each other in years. Well, Scott hasn't seen her. She's been watching out for him and his friends in Beacon Hills ever since she was bit by an alpha, Peter Hale.
She watches her brother in secret with her friend Nick while Scott has no idea that she's around. Or that she's even a werewolf like him for that matter.
Once she finally makes herself known to him he doesn't recognize her, which is exactly what she wants. He hasn't seen Airis since they were kids and she refuses to let her dad take pictures.
A lot of bad things are starting in Beacon Hills and Airis has to return to her childhood home, but she's afraid of either of her parents seeing her because she doesn't want her brother or his friends to know who she is. She does this to protect all of them.
You see, where Airis goes, danger is soon to follow. Her and Nick have many enemies and she doesn't want them to become her brothers as well. He has enough to deal with as it is.