Maid-san wa Kyuuketsuki

Fifteen-year-old Alfred Saionji, heir to the venerable Saionji family, endures a strict disciplined life, in order to become a “first-class, respectable gentleman.” His only companion is his maid, Maggie, a cool and beautiful young woman who brings color to Alfred's life. But in fact, Maggie is a vampire. Once she tastes blood, she reveals her hidden sexy nature, and Alfred is soon offering up his own blood to her.... But the truth is that vampires and humans are “incompatible” in this world. This is a story of “pure love” between a boy who seeks the strength to protect the girl he loves, and a clumsy vampire maid who is in love with him.

(Source: Champion Cross, translated)