Rui Kamishiro is a university professor of higher mathematics. He's young and single, and apparently some people are attracted to him. But he's not particularly interested in anyone. Since childhood, he's had a condition that causes him to have too much blood, and he regularly took himself to the hospital for treatment. But it turned out that the student who often studies with him is a vampire. Now they help each other and become closer. Tsukasa is 21