Hazuki, also known by her alternate persona Luna, is the main female protagonist and a fourteen-year-old vampire who initially appears imprisoned within the ancient castle of Schloss Schwartzquelle in Germany. While her physical body looks like a young teenager, her true chronological age is far older due to her nature as a vampire, having lived for over a thousand years. In terms of appearance, she has long, dark hair often rendered as raven-black, dark purple, or deep blue and typically wears cat ears as a signature accessory, preferring white ones. Her outfits frequently fall under the Elegant Gothic Lolita style, though she is also seen in kimonos and casual clothing. A notable visual indicator of her mental state is a pendant she wears; the position of this locket, which bears a crescent moon design, helps signal which personality is in control.

Hazuki has a dual nature that is central to her character. The dominant Hazuki personality is selfish, spoiled, proud, and prone to throwing temper tantrums, though she is also described as adorable and capable of being charming when she wants to manipulate someone to her advantage. The Luna personality serves as her cold-hearted and domineering alter ego, implanted in her by her father to make her more tractable and obedient. Luna typically only emerges during the full moon through the use of a special pendant, but she can also communicate with Hazuki telepathically during moments of intense stress and can forcibly take control of Hazuki's body. Originally, Hazuki had no memory of the actions taken by Luna, but this changes over the course of the story.

Her primary motivation is the search for her mother, from whom she was separated before being imprisoned in the German castle. Because she is a rare Daywalker—a vampire who, unlike others of her kind, can withstand sunlight—her family is desperate to retrieve her and keep her hidden, as any other vampire who drank her blood could potentially gain this ability. This unique trait makes her a target for other vampires and is the driving force behind much of the conflict in the narrative.

The story revolves around her escape from the castle with the help of the photographer Kouhei Morioka and her subsequent life in Japan, living with his family. Although she bites Kouhei to make him her slave through a vampires kiss, the attempt fails because Kouhei is a Vampire Lover, meaning he is naturally immune to the binding power of her bite. Despite her constant demands that he obey her as her servant, Kouhei refuses to do so, leading to frequent arguments between the two that are a major source of both comedy and character development. Over time, she comes to truly care for him and falls in love with him.

Key relationships significantly shape her development. Beyond Kouhei, she forms a strong bond with his grandfather, Ryuuhei Morioka, who invites her to live with the family and acts as a teasing but supportive father figure. Later in the series, she is introduced to her younger half-sister, Artemis, also known as Arte. Their relationship begins very rocky, driven by Arte's jealousy and attempts to steal Kouhei away, but eventually develops into a sisterly bond of complete trust and love after they reconcile.

Throughout the series, Hazuki undergoes significant character development, growing from a lonely, bratty captive into someone capable of deep affection and self-sacrifice. Thanks to Kouhei's influence, her true Hazuki personality becomes stronger, and she gradually gains the ability to resist Lunas control. This internal struggle culminates in the two personas eventually merging, allowing her to finally break free of Lunas influence and become whole.

Beyond her rare immunity to sunlight, Hazuki possesses typical vampiric abilities including a hypnotic gaze and enhanced physical traits. She also demonstrates powerful telekinetic abilities. A distinct physical trait is that her eyes, normally blue, turn violet after she drinks blood.