This is a The Originals story where there's a girl that comes to New Orleans claiming to be Henrik Mikaelson twin sister. She comes face to face with her older brother Klaus.
Niklaus Mikaelson had a daughter before Hope. And although he
took her in he never really paid any attention to her because he never
believed that she was his own daughter. This only got worse when Hope came along.
The plot, Dawn and any additional characters that are not part of The Originals TV show belongs to me.