At a certain point, you learn that Alrik's henchman who created and now controls the dragon isn't who you thought it was. He was a wizard whose mind was taken over by Alrik. In fact, this wizard (the one whose mind is being manipulated) is, in fact, Serilda's father Valdemar. (She has never met him until this point.)
He struggles against the spell that controls him and begs for your help. He wants his mind and soul back. In short, he has experienced Undeserved Misfortune, and he'll thus have Rooting Interest, too.
In the first few minutes of the film The Fugitive, Harrison Ford's character fails to prevent the murder of his wife. Then he's arrested, charged with that murder, and found guilty. Because of his Undeserved Misfortune, we strongly identify with him.