Makoto Okazaki, a nondescript high school student, is frequently targeted by his classmates and made to carry out their menial demands. One fateful night, his life takes an unexpected turn when a mysterious girl attacks and feeds on his blood. After finishing her meal, she offers Makoto a choice: adapt to her lifestyle or else face certain death.
When he wakes up in the hospital, Makoto is disoriented and overwhelmed by an unrelenting thirst that water cannot satisfy. The bright light blinds him, and he struggles to comprehend what has occurred.