Hitokuchi Choudai 

Yui Sasame, a descendant of vampires, feels out of place in her high school class. Unable to fit in with her human classmates, she's often late to school—something for which the class representative, Sekiya, relentlessly criticizes her. One day, angered by Sekiya's nagging, a dark impulse flickers through Yui's mind... "Maybe I should just... suck him dry." But that thought marks the beginning of something far more dangerous—an ecstasy said to surpass sexual pleasure a hundredfold. Thus begins the tragic tale of those consumed and undone by their own desires.