Hasekura Kouhei transfers into Shuchikan Academy, a prestigious public school in the style of an English six-year school encompassing junior-high and high school students. The school is on an island named Tamatsu Island off-shore from mainland Japan, and the only way to get there is by boat. Soon after transferring, he discovers that Sendou Erika, one of the students in the class next to his, is in fact a type of vampire.

[Edited from Wikipedia]