Mito Yamamoto is a teenage orphan who lost her parents in a house fire when she was a child. After spending years being passed between relatives who viewed her as a burden, she is eventually kicked out and left homeless. Forced to fend for herself, she secretly sleeps at the ramen shop where she works as a waitress until she is fired for doing so. To protect herself from unwanted attention and harassment, she begins to cross-dress as a boy, cutting her hair short and presenting herself as male. Despite her difficult circumstances, she is a resilient and determined person, though she often feels lonely and desperate for a place to belong.

Her life changes when she stumbles into a cafe called La Fraise and accidentally breaks a vase, cutting her finger. One of the handsome waiters, Ruka Saotome, tends to her wound and, believing her to be a boy, licks the blood from her cut. He finds the taste disgusting and rejects her. Later, feeling utterly hopeless, Mito contemplates suicide by jumping from a bridge. She slips and falls, but Ruka rescues her, revealing himself to be a vampire. He explains that the blood of someone who is unloved has a bitter taste, and that he cannot drink from women for mysterious reasons. He proposes that Mito become his thrall—a willing blood donor—and that he will love her to make her blood sweeter. In return, she will have a home. Mito agrees and moves into the dormitory of Hijirigaoka Boys' Academy, where she continues to disguise herself as a male student. She also takes a job at the cafe alongside Ruka.

Over the course of the story, Mito develops genuine romantic feelings for Ruka, and their relationship deepens as she struggles to keep her true gender a secret. Her primary motivation is the desire for stability, safety, and a sense of belonging, which she gradually finds in her bond with Ruka. She grows from a lonely, isolated orphan into someone who actively cares for another person and is willing to face challenges to protect their connection. Notable abilities include her skill at maintaining her male disguise and her role as a thrall, meaning her blood serves as Ruka’s primary food source. The quality of her blood is directly influenced by her emotions—when she feels loved and secure, it becomes sweeter for Ruka. She has no supernatural powers of her own, but her relationship with Ruka places her at the heart of the supernatural and romantic conflicts in the story.