Ichijou-san wa Kao ni Deyasui

Ichijo-san is a beautiful girl from a wealthy family who treats everyone, including her introverted classs-mate Mahiro, kindly. But she has a secret: she is a vampire. When Mahiro accidentally discovers that Ichijo is a vampire, he begins to eat lunch with her. Ichijo-san tells him that vampires can just drink animal blood now, but she still seems very interested in human blood....... The exchange unfolds between Ichijo-san, who cannot hide her desire to suck human blood, and Mahiro, who just enjoys having lunch with her.

(Source: Natalie.mu, translated)