Aoi Shinozuka is a fifteen year old girl who enrolls at the same high school as the main character Rihito Tatsuno. She has a pure and innocent personality, which makes her trusting to a fault, a trait she shares with her classmate Rihito. Because of this, she easily believes the outlandish claim from another classmate, Ranmaru Mori, that he is a vampire. Aoi is also an otaku for vampire lore, which fuels her fascination with the supernatural. She has a distinct appearance with short hair and a straight, blunt fringe.

On the day of the high school entrance ceremony, Aoi literally bumps into Rihito on the way to school. He treats her with kindness, and he instantly develops a crush on her, marking her as his first love. However, the romantic dynamic becomes complicated when Ranmaru, who is secretly a centuries-old vampire intent on preserving Rihito’s purity, attempts to confront Aoi to scare her off. Instead of being frightened, Aoi becomes captivated by Ranmaru, especially after he saves her from a dangerous situation involving an exhibitionist. This rescue solidifies her growing affection, and she soon finds herself falling in love with him. She often refers to Ranmaru with the respectful and affectionate title of Vampire-sama. From Ranmaru’s perspective, his hostile glares are meant to be threatening, but Aoi misinterprets them as the intense gaze of a vampire watching her, reinforcing her positive feelings.

Aoi’s role in the story is primarily that of a catalyst for comedic misunderstandings and romantic tension. Her presence creates a one-sided love triangle where Rihito loves her, but her own affections are directed toward Ranmaru, who is solely focused on Rihito. This dynamic directly frustrates Ranmaru’s plan to keep Rihito from any romantic entanglements that might compromise the taste of his blood. Aoi’s brother, Ken Shinozuka, who is nicknamed Franken, is a third-year student at the same school and the leader of a group of troublemakers. He is extremely strong and overprotective, which leads him to confront Ranmaru over his involvement with his sister. As the story progresses, Aoi remains largely oblivious to the depth of Rihito’s feelings for her, while she continues to be torn between seeing him as a friend and pursuing her fascination with Ranmaru. Her primary ability lies not in combat or supernatural powers, but in her naive and pure-hearted sincerity, which inadvertently drives the chaotic and humorous plot.