Fortune Arterial: Akai Yakusoku follows Kohei Hasekura, who transfers to a prestigious public school that follows a six‑year English‑style system, covering both junior high and high school. The school sits on Tamatsu Island, located off the mainland of Japan, and can only be reached by boat. Shortly after arriving, Kohei learns that Sendo Erika, a student in the neighboring class, is actually a vampire.