The vampire could be a love interest. A normal student falls for the vampire, not knowing their true nature at first. As the relationship develops, the vampire has to struggle with their feelings and their instinct to feed. This creates a lot of drama and tension in the high school story, like when they go on a date and the vampire has to resist the urge to bite the other person.
A vampire can fit in as an outcast. They might be shunned by some students because of their different behavior, like not eating normal food or being active only at night. But they could also attract a small group of curious friends who are intrigued by their mystery.