Their relationship could develop uniquely if they start off as rivals. Maybe they both want to be the top student in a certain class or get a particular assignment. But as they compete, they start to notice each other's good qualities. For example, Rose might see Christian's determination and intelligence, and Christian might see Rose's loyalty and courage. This could gradually turn their rivalry into a friendship and then something more.
One way to develop their relationship uniquely is through a shared interest in art. Suppose Christian is secretly an artist and Rose discovers his work. They start to bond over their love for art, which is different from the typical vampire - fighting or academy - related things that usually bring people together in the Vampire Academy world. They could have deep conversations about the meaning of art and how it relates to their lives as vampires or dhampirs. As they do this, their relationship becomes more profound.
A very different approach could be that they are forced to work together in a magic - based project. They have to combine their powers in a way that is completely new to them. At first, they struggle and argue because their powers are so different. Rose's dhampir strength and Christian's magic don't seem to mesh well. But as they keep trying, they find a way to make it work. This shared struggle and discovery not only brings them closer but also gives them a connection that is unique to just the two of them.