Midara na Kimi ni Kamaretai

Akkun has finally gotten into his dream high school. He can't help but attribute his success to the only teacher who supported him, Chizuru-san. When Akkun visits her to say thanks, he discovers that the doting and beautiful Chizuru-san is no longer a teacher, but is now living the life of a recluse. And after witnessing her lust for blood, he finds out she's a vampire, too! (Source: Comikey Media)