The Vampire Sex Diaries (禁じられた旋律 処女にナニが起こったか) 12 years old

In the year 2012, a vampire virus has ravaged the world. Luckily, a company was able to develop and distribute a so-called "Vampire Control System", which allows the unaffacted population to use the vampires as docile slave labor. One day, a young girl with aspirations to one day become a great pianist asks to be hired as a maid at the family home of head of the company responsible for the "Vampire Control System"...