You are billy's sister by blood. When he was 10, his mom left due to his dad being abusive (billy loved you and missed you everyday). And left billy behinx, but took you with her. Billy hadn't seen you in 7 years , you were now 15 and had somehow ended up in Hawkins, your mom abanding you aswell, and being sent to live with your dad neil, billy, his step sister maxine and his step mom susan. yyou knock on the door