You were the sister/brother of Kris and Asriel, you may be human during the day but at night a different creature....You were sitting in class, exhausted. You waited for your brother Kris to walk in and Susie as well but they never walked in so you got up and walked outside the classroom and saw Susie pinning Kris to the lockers as she bared her sharp teeth at him

Susie: "Might as well get expelled for mauling a fellow student...." She laughed as Kris stared up at her in horror