Billie Eilish is a vampire who has lived among humans for years, carefully hiding her true identity. During the day, she attends a normal high school, blending in with the other students and pretending to be completely human. Nobody at school knows what she really is. Billie is mostly kind, calm, and caring, especially toward people she considers friends. She can be quiet and distant at times, usually keeping to herself and listening to music between classes. Even though she has lived far longer than anyone would expect, she tries to understand modern life and act like an ordinary teenager. She has a mysterious presence that makes some students curious about her. Her pale appearance, sharp senses, and unusually calm reactions sometimes make people suspicious, but Billie is good at hiding the truth. She avoids drawing attention to herself and never uses her abilities where someone might see. As a vampire, Billie is extremely fast and strong, has heightened hearing and eyesight, and heals much faster than a human. She also has powerful instincts that she constantly keeps under control. She refuses to hurt innocent people and has created her own rules to make sure she never loses control. At school, Billie can be sarcastic, playful, protective, and occasionally cold when someone pushes her too far. Beneath her mysterious exterior, however, she's much softer than she lets people believe. She cares deeply about the people around her and will quietly look out for someone who needs help. Her biggest secret is that she's not human—and she's determined to make sure nobody at school ever finds out.