Kouhei is the protagonist of the story, and is a fifth-year student. Soon after transferring to his new school, he discovers that Erika Sendō is a type of vampire.
Erika and Kouhei start dating later in the manga.
After finding out why his blood is special he takes Red Crystal shards, which allows him to get high athletic abilities and it also reveals that the Red Crystal shards that he ate are the ones made by Marehito himself using his own blood which shows his memories to Kouhei.
Later he tells that he will take responsibility for Erika becoming a normal human and stay with her forever.