In the town of Kashinokidai, where humans coexist alongside yokai, ghosts, robots, and other supernatural beings under the watch of a local land god, a vampire high school girl named Luna Ishikawa transfers into Kashinokidai High School. To her classmates, Luna appears to be the epitome of a cool, mysterious, and untouchable beauty—an image she works hard to maintain. In truth, she is clumsy, prone to snacking to stave off hunger, and fundamentally incapable of performing the most basic vampire act: sucking blood properly. She leaves messy wounds, hurts her donors, and can never get the technique right.

Her secret is discovered by her seatmate, Tatsuta Otori, a self-described background character who notices her fumbling during cleaning duty. Instead of being frightened, Otori feels a strong urge to help. He offers Luna the chance to practice sucking blood on him, both to improve her skill and to satisfy her hunger. When Luna bites him, he experiences an unexpectedly pleasant, almost maternal affection for her. The two strike a deal: Luna practices on Otori in secret, and in return he will train her to be a proper vampire. This arrangement forces them to act as strangers in public while engaging in increasingly intimate and awkward practice sessions in private.

As the story unfolds, other classmates learn Luna's secret. The energetic and forward Eiko Sakuma overhears Otori and Luna and, rather than being disillusioned, finds Luna's incompetence even more endearing. She eagerly volunteers to be bitten as well. The serious and reserved Misa Kusunoki also becomes drawn into Luna's world after stumbling upon her in a vulnerable moment. Together, these friends form a small circle that helps Luna navigate both everyday high school life and her vampire struggles.

The narrative progresses through a series of school-year events that test Luna's abilities and her growing bonds with Otori and her friends. During the sports festival, Luna dominates on the court but shrinks into a tiny, vulnerable form when exhausted. In the culture festival, class 2-A operates a café while Luna's house, a dungeon-like building, provides props. A summer trip to the beach gives Luna her first experience of a normal vacation, and a birthday party for Otori pushes her to attempt cooking and planning. Throughout these arcs, Luna gradually sheds her carefully crafted cool persona and reveals her true, awkward, and affectionate self. Her relationship with Otori deepens as he becomes not only her practice partner but also her emotional anchor. Meanwhile, the land god and school chairperson, Misuzu Kirihata, watches over Luna with maternal care, adding another layer of protection to the chaotic but warm world of Kashinokidai.