Shion no Ketsuzoku ~Kono Futashika na Sekai to Tenshi-tachi no Rondo~

The female magicians of the Shionji family are designated as protectors of the royalty. They are actually vampires called Apneas. The only male in the family, Mikoto, lives deep in the forest with his twin older sister Ariha, his relative Shizuka and a sexroid Nowem. The girls attend the boarding school Shikyou Gakuen, however their normal lives are soon shattered by the appearance of a Catholic sister, Sofia, who is intent on exterminating all vampires, including the Shionji.